The following is a chronology of key events in U.S.-Iran relations since the 1979 revolution.
Feb. 14 – Students stormed the U.S. Embassy in Tehran, but were evicted by the deputy foreign minister and Iranian security forces.
Aug. 10 – Iran canceled a $9 billion arms deal with the United States made during the shah's reign.
Nov. 4 – Students belonging to the Students Following the Imam’s Line seized the U.S. Embassy in Tehran. The hostage crisis lasted 444 days. On Nov. 12, Washington cut off oil imports from Iran. On Nov. 14, President Carter issued Executive Order 12170 ordering a freeze on an estimated $6 billion of Iranian assets and official bank deposits in the United States.
April 7 – The United States cut off diplomatic relations with Iran.
April 25 – The United States attempted a rescue mission of the American hostages during Operation Eagle Claw. The mission failed due to a sandstorm and eight American servicemen were killed. Ayatollah Khomeini credited the failure to divine intervention.
Jan. 20 – After weeks of mediation by Algeria, Washington and Tehran agreed to the Algiers Accord to end the hostage crisis. The United States agreed to release frozen Iranian assets and not to intervene in Iranian affairs, in exchange for the release of 52 American hostages. Both countries agreed to end lawsuits. All claims would be referred to international arbitration at a new Iran-U. S. Claims Tribunal in The Hague.
July 19 – American University of Beirut President David Dodge became the first of several Americans to be taken hostage over the next nine years. He was the only one taken from Lebanon to Iran, where he spent one year in prison.
Oct. 23 – The United States accused Iran of aiding the suicide bombing at the barracks of U.S. Marine peacekeepers in Lebanon, which killed 241 U.S. military personnel, the largest loss to the American military in a single incident since Iwo Jima in World War II.
Jan. 23 – The Reagan administration put Iran on the State Department list of governments supporting terrorism.
March – An Iran-supported militia in Beirut again began abducting American hostages, including CIA station chief William Buckley, who died in captivity.
Apr. 1 – Washington warned Iran it would be held responsible if American hostages were harmed. By mid-summer, Washington had begun behind-the-scene diplomatic efforts that led to the arms-for-hostage swap.
June 2 – During a visit to Japan, Parliamentary Speaker Akbar Hashemi Rafsanjani called on the United States to restore relations with Iran. Later that month, he played a role in ending the hijacking of TWA 847, the 17-day hostage ordeal of 39 Americans in Beirut.
Aug. 14 – A shipment of U.S. TOW antitank missiles was sent to Tehran from Israel as part of the secret arms-for-hostage swap. The same day, Rev. Benjamin Weir became the first of three American hostages to be freed in Lebanon.
Nov. 22 – A shipment of HAWK anti-aircraft missiles was sent to Tehran from Israel as the second phase of an arms-for-hostage swap, but the deal fell far short of what was promised and Iran ordered a refund of payment and a resupply.
Jan. 17 – President Ronald Reagan signed a special finding to permit negotiations with Iran on hostages and to help promote “moderate” elements in Tehran. This was followed by a shipment of 1,000 TOW missiles to Iran at the end of February.
May 25-28 – Former national security adviser Robert McFarlane and Lt. Col. Oliver North made a secret trip to Iran to deliver arms. In July, American hostage Father Lawrence Jenco was freed in Lebanon. On Aug. 3, the United States delivered new HAWK missiles to Iran.
September – Two more Americans were taken hostage in Lebanon. On Sept. 19-20, an Iranian emissary related to Rafsanjani visited Washington for talks on arms, hostages and improved relations.
October – During Operation Nimble Archer, the United States attacked Iranian oil platforms in retaliation for an Iranian attack on the U.S.-flagged Kuwaiti tanker, Sea Isle City.
October – American writer Edward Tracy was taken hostage in Lebanon. A few days later, the United States provided 1,000 TOW missiles to Iran. On Nov. 2, American hostage David Jacobsen was freed in Beirut.
Nov. 3 – The Lebanese magazine Ash-Shiraa exposed secret dealings between Iran, Israel and the United States, which became known as the “Iran-Contra affair.”
April 7 – Parliamentary speaker Rafsanjani said that Iran would try to mediate the release of American hostages in Lebanon if the United States showed “good will” by unfreezing Iranian assets in the United States. On May 13, the United States returned $450 million in frozen assets.
Apr. 14 – The frigate USS Samuel B. Roberts was badly damaged by an Iranian mine. U.S. forces responded with Operation Praying Mantis on April 18, the U. S. Navy’s largest engagement of surface warships since World War II. Two Iranian oil platforms, two Iranian ships and six Iranian gunboats were destroyed.
June 19 – The USS Vincennes shot down an Iranian passenger plane, killing 290 passengers and crew on board.
Nov. 3 – The United States returned $567 million of frozen Iranian assets, in accordance with the Algiers Accord of 1981. American officials denied the deal was linked to Iranian President Rafsanjani's offer to help in the release of hostages in Beirut. Iranian assets valued at $900 million remained frozen.
Jan. 20 – In his inaugural address, George H. W. Bush said, “good will begets good will,” in reference to Iran and American hostages held by pro-Iranian Hezbollah in Lebanon.
Dec. 4 – Terry Anderson, the last American hostage in Lebanon, was freed after Iranian intervention.
April – President Clinton gave what Congress later termed a “green light” for Iran to transfer arms to the Muslim government of Bosnia fighting Serbian forces. The permission came despite a United Nations arms embargo against Iran. In 1996, the Senate Intelligence Committee and the House Select Subcommittee confirmed the U.S. role in the Iranian arms transfer.
March 15 – The Rafsanjani government offered a billion-dollar contract to U.S. oil giant Conoco to develop two offshore oil fields, which was blocked after President Clinton signed an executive order banning U.S. investment in the Iranian oil industry.
May 6 – President Clinton issued a total embargo of U.S.-Iran trade and investment over the country’s alleged sponsorship of "terrorism," nuclear ambitions, and hostility to the Middle East peace process.
June – Iran was suspected of masterminding the June 25 bombing of Khobar Towers, a U.S. Air Force housing complex in Saudi Arabia. Subsequently, the Clinton administration sent a letter to President Khatami, transmitted by the foreign minister of Oman. The letter indicated that Washington had direct evidence of the Revolutionary Guards’ involvement in the attacks. The message also stated that the United States wanted to work toward better relations with Iran. Tehran’s response was brusque, denying the allegations.
Aug. 4 – President Clinton signed into law the Iran-Libya Sanctions Act (ILSA), which penalized foreign companies doing business with the United States that also invested more than $20 million in the Iranian oil industry.
Jan. 7 - In an interview with CNN, President Khatami said Iran had an “intellectual affinity with the essence of American civilization” because it was also trying to construct a system based on the pillars of “religiosity, liberty, and justice.” He called for both countries to try to bring down the “wall of mistrust.”
March 17 – In a speech, Secretary of State Madeleine Albright apologized for America's role in the 1953 overthrow of democratically elected Prime Minister Mohammad Mossadegh. She admitted that the coup, which put the shah back on the throne after he fled into exile, “was clearly a setback for Iran's political development.” The Clinton administration partially lifted sanctions on Iranian carpets and foodstuffs. But Iran denounced the goodwill gesture because Albright’s speech ended by criticizing Iran’s domestic policies.
Sept. 27 – Ayatollah Khamenei and President Khatami condemned the al Qaeda 9/11 attacks on New York and Washington D.C.
October 8 – Supreme Leader Khamenei condemned U.S. strikes on Afghanistan. At the same time, Iran agreed to perform search-and-rescue missions for U.S. pilots who crashed on Iranian soil during the war.
October-December – After the U.S. intervention in Afghanistan ousted the Taliban, Iran cooperated with the United States, Russia and India in providing support for the Northern Alliance opposition to bring down the Taliban. Iranian diplomats met with their U.S. and other Western counterparts in Bonn to form a new Afghan government. Iran also worked with the United Nations to repatriate nearly 1 million Afghan refugees.
Jan. 29 – In his State of the Union address, President George W. Bush referred to Iran, Iraq and North Korea as an “axis of evil.”
March – Following the U.S.-led invasion and occupation of Iraq, Syria and Iran intensified their cooperation to ensure they would not become Washington's next targets. They expanded bilateral defense cooperation and support to insurgent groups to tie down U.S.-led forces in Iraq.
May – A Swiss diplomat relayed Iranian conditions for bilateral talks to the Bush administration shortly after the U.S. invasion of Iraq, but it was not taken seriously in Washington.
Dec. 26 – A devastating earthquake hit the southeastern city of Bam, killing more than 26,000 people. On Dec. 30, the United States flew in an emergency response team. The military aircraft were the first U.S. planes to land in Iran in 20 years.
June 21 – Iran arrested six British sailors -- part of the U.S.-led force in Iraq—for trespassing into Iran’s territorial waters. As a blow to Britain, Tehran paraded the servicemen through the city and forced them to apologize. They were released three days later, after negotiations.
June – Former Revolutionary Guards commander and presidential candidate Mohsen Rezaei said Iran played a more significant part in the overthrow of the Taliban than given credit for by the United States. Washington consistently denied that Iranians made meaningful contributions.
June 16 – Iran and Syria signed an agreement for military cooperation against what they called the "common threats" presented by Israel and the United States. In a joint press conference, the defense ministers from the two countries said their talks had been aimed at consolidating their defense efforts and strengthening mutual support.
May 8 – President Ahmadinejad sent President Bush an 18-page letter.
Feb. 8 – Ayatollah Khamenei warned that Iran would target U.S. interests around the world if it came under attack over its nuclear program.
May 28 – Iran and the United States held the first official high-level talks in 27 years. The meeting, which took place in Baghdad, came after Iraq hosted a security conference attended by regional states and the permanent members of the U.N. Security Council. The talks were on Iraq’s security and were followed by two more rounds in July and November. The United States urged Tehran to stop supporting Shiite militias in Iraq. The talks ultimately did not lead anywhere and stopped after three meetings.
Sept. 6 – NATO forces in Afghanistan intercepted a large Iranian shipment of arms destined for the Taliban. The shipment included armor-piercing bombs. Washington said that the shipment’s large quantity was a sign that Iranian officials were at least aware of the shipment, even if not directly involved. Tehran denied the charges.
October – U.S. military commander Gen. David Petraeus claimed Iran was triggering violence in Iraq. Petraeus also accused Iran’s ambassador to Iraq of being a member of the elite Qods Force, a wing of the Revolutionary Guards responsible for foreign operations.
Oct. 25 – Washington imposed the most sweeping unilateral sanctions since the takeover of the U.S. Embassy in 1979. It sanctioned the Revolutionary Guards and a few Iranian banks, and individuals believed to have links to nuclear and terror-related activities.
Sept. 20 – New York City officials denied President Ahmadinejad’s request to visit the site of Sept. 11 attacks during his visit to the United Nations.
December – A U.S. National Intelligence Estimate concluded that Iran halted its nuclear weapons program in 2003.
April – The United States accused Iran of continuing its alleged support of Taliban insurgents.
Sept. 24 – President Ahmadinejad spoke at the United Nations and Columbia University, where he criticized U.S. policy and said there were no homosexuals in Iran.
Nov. 6 – President Ahmadinejad wrote President-elect Barack Obama congratulating him on his election and urging “real change.”
Feb. 10 – In a speech marking the 30th anniversary of the Islamic Revolution, President Ahmadinejad welcomed talks with the United States based on “mutual respect and in a fair atmosphere.”
March 20 – President Barak Obama sent a Nowruz (Iranian New Year) message to the Iranian people and government that called for better relations. He also said that Iran’s place in the international community “cannot be reached through terror or arms, but rather through peaceful actions.”
March 20 – Ayatollah Khamenei referred to Obama’s speech as deceptive. In light of recent sanctions, he said Iran would judge the United States by its actions and not by its words.
May 1 – Iran rejected the April 2010 report by the U.S. State Department that designated Iran as the “most active state sponsor of terrorism.” Tehran said that the United States could not accuse others of terrorism after its actions at Iraq’s Abu Ghraib prison and Guantanamo Bay.
May – President Obama sent a letter to Ayatollah Khamenei before Iran’s June presidential elections that called for improved relations through “co-operation and regional bilateral relations.” Khamenei briefly mentioned the letter in his Friday sermon.
September – An Iranian news website reported a second letter sent by President Obama to Ayatollah Khamenei.
October – Iran blamed the United States and Britain for involvement in suicide bombings that killed 15 members of Iran’s Revolutionary Guards in southeastern Iran. The attack was carried out by the Sunni Muslim rebel group Jundollah, which Iran claimed was funded by the United States. The group had carried out a similar attack, killing 40, around five months earlier.
Oct. 21 – Iran agreed to a U.S.- and U.N.-backed deal designed to provide fuel for Tehran’s research reactor for medical needs and to remove a large part of Iran’s enriched uranium from its control. The deal called for the transfer of 1,200 kg of low-enriched uranium to Russia for further enrichment and then to France to produce fuel for the Tehran Research Reactor. But Iran later backed off from the agreement.
December – Gen. Petraeus accused Iran of backing Shiite militants in Iraq and giving a "modest level" of support to the Taliban in Afghanistan.
March 20 – President Obama sent a second Nowruz message to the Iranian government and people. The message encouraged dialogue between the two countries and criticized Iran’s human rights violations during post-election protests.
April 13 – President Ahmadinejad disclosed that he wrote a second letter to Obama. “Obama only has one way to tell the world that he has created change, and that is Iran,” he said in a televised interview.
June 26 – The U.S. Congress passed tough new sanctions against Iran’s energy sector and IRGC affiliated companies. Congress also called for penalties against companies that export gasoline and other refined energy products to Iran.
Dec.6-7 – Iran met in Geneva with members of the U.N. Security Council and Germany for negotiations over Iran’s nuclear program. The group agreed to meet again in January 2011 in Istanbul.
Jan. 21-22 – Nuclear negotiations held in Istanbul between P5+1 countries and Iran failed after Tehran refused to discuss transparent limits on its uranium enrichment program.
Feb. 24 – The United States imposed new sanctions on two top Iranian officials for engaging in “serious human rights abuses” since the disputed 2009 election.
March 20 – President Obama sent a third Nowruz message to Iran, directed specifically at Iran’s youth. The President addressed Iran’s young people, saying, “your talent, your hopes, and your choices will shape the future of Iran, and help light the world. And though times may seem dark, I want you to know that I am with you.”
May 23-24 – The E.U. imposed sanctions on more than 100 individuals and companies tied to Iran's nuclear program, while the United States sanctioned seven foreign companies involved in supplying Iran refined oil as well as sixteen firms and individuals involved in the missile and nuclear program.
Oct. 11 – The U.S. Treasury Department designated five individuals, including four senior Islamic Revolutionary Guard Corps-Qods Force officers connected to a plot to assassinate the Saudi Arabian Ambassador to the United States.
Oct. 12 – The U.S. Treasury Department designated the Iranian commercial airline Mahan Air pursuant to Executive Order 13224 for providing financial, material and technological support to the Islamic Revolutionary Guard Corps-Qods Force.
Nov. 21 - The United States, United Kingdom, and Canada announced bilateral sanctions on Iran. The United Kingdom severed all ties with Iranian banks.
Dec. 4 – Iran captured a U.S. dronenear the northeastern city of Kashmar and refused to return it to the United States.
Dec. 15 – The U.S. Senate passed new sanctions on Iran’s central bank.
Dec. 6 – The United States launched its Virtual Embassy Tehran website to provide a means for direct communication with Iranians.
Dec. 13 – The United States sanctioned two senior Iranian military officials for responsibility for or complicity in serious human rights abuses.
Dec. 20 – The United States issued new sanctions against front companies linked to Iran’s missile program.
Jan. 11 – The United States sanctioned three Chinese, UAE, and Singapore firms under the Amended Iran Sanctions Act.
Feb. 6 – The United States imposed sanctions on Iran’s Central Bank.
Feb. 16 – The United States imposed sanctions on Iran’s Intelligence Ministry.
March 6 – The P5+1 countries agreed to resume talks with Iran over its nuclear program.
March 20 – President Obama sent a fourth Nowruz message to the Iranian government and people. The message accused Iran of having an “Electronic Curtain,” criticizing the Iranian government’s internet censorship.
April 14 – P5+1 diplomats met in Istanbul with Iranians to discuss Tehran’s promised “new initiatives” on its nuclear program.
May 1 – The White House issued an Executive Order targeting foreign sanctions evaders.
May 23-24 – The P5+1 held inconclusive talks with Iran in Baghdad.
June 18-19 – The P5+1 held inconclusive talks with Iran in Moscow.
June 11 – Secretary of State Hillary Clinton announced Iran sanctions exceptions for India, Malaysia, Republic of Korea, South Africa, Sri Lanka, Turkey and Taiwan.
July 12 – The United States announced broad new sanctions on Iranian front companies and banks linked to the Tehran’s nuclear and missile programs.
July 31 – The United States announced new sanctions on Iranian oil and foreign financial institutions that facilitate transactions for Iranian banks.
Aug. 2 – The U.S. Congress voted to impose new sanctions on Iran that target companies aiding Tehran’s energy sector. The Iran Sanctions, Accountability, and Human Rights Act of 2012 differs from President Obama’s July 31 executive order by targeting companies conducting business with Iran’s national oil company and tanker fleet, such as insurers and shippers.
Aug. 10 – The United States imposed sanctions on a Syrian state-run oil company, Sytrol, for conducting business with Iran’s energy sector.
Aug. 12 – The United States offered aid to Iran after two earthquakes reportedly hit almost 200 villages near the northwest city of Tabriz.
Sept. 28 – The U.S. State Department revoked the Mujahedin-e Khalq’s (MEK) designation as a Foreign Terrorist Organization. The leftist group had killed six Americans in Iran in the 1970s and attempted an attack against Iran’s U.N. mission in 1992. The State Department then added it to the terrorism list in 1997. But the MEK renounced violence in 2001 and no terrorist attacks have been positively linked to the organization for more than a decade.
Oct. 9 – The United States moved to tighten loopholes in its Iran sanctions. President Obama’s executive order aimed to implement additional punitive measures that he signed into law on August 10, 2012.
Nov. 8 – The U.S. Treasury Department sanctioned 17 individuals and entities related to the Iranian government’s human rights abuses, its support of terrorism, and Iran’s Revolutionary Guards.
Nov. 30 – The U.S. Senate unanimously approved new sanctions on Iran’s energy and shipping sectors.
Dec. 4 – Iran reported that it had captured a U.S. drone that entered its airspace over the Gulf, but the United States denied this claim.
Dec. 7 – Secretary of State Hillary Clinton announced the renewal of Iran sanctions exceptions for China, India, Malaysia, Republic of Korea, Singapore, South Africa, Sri Lanka, Turkey and Taiwan.
Dec. 13 – The U.S. Treasury and State Department imposed sanctions on seven Iranian companies and five individuals for “proliferating weapons of mass destruction” pursuant to Executive Order 13382.
Dec. 21 – The U.S. Treasury froze the assets of four Iranian companies and one executive for links to Tehran’s missile and nuclear programs.
Feb. 2 – Vice President Joe Biden said that the United States was prepared to hold direct talks with Iran to resolve tensions over its controversial nuclear program.
Feb. 6 - The U.S. Treasury Department imposed new sanctions on the Central Bank of Iran and other financial institutions to restrict Tehran’s ability to spend oil revenues. It also designated one individual and four entities for involvement in censorship activities.
Feb. 7 – Iran released footage it claimed to have salvaged from a U.S. drone that it reportedly downed in 2011.
Feb. 7 – Supreme Leader Ayatollah Ali Khamenei rejected the offer by Vice President Biden for direct talks. “Some naïve people like the idea of negotiating with America. However, negotiations will not solve the problem,” he said in a speech to Iranian Air Force commanders.
Feb. 11 – The U.S. Treasury Department imposed new nonproliferation sanctions on entities and individuals from Belarus, China, Iran, Sudan, Syria, and Venezuela. Credible information indicated that they had transferred to, or acquired from, Iran, North Korea, or Syria, equipment and technology related to weapons programs.
Feb. 16 – Supreme Leader Ayatollah Ali Khamenei claimed that although Iran has no intention to build nuclear weapons, “America would not have been able to stop the Iranian nation in any way” in speech in Tabriz, Iran.
Feb. 20 – Ambassador Mohammad Khazaee welcomed recent U.S. calls for direct talks. He outlined steps the United States could take to prove its good faith, such as “discarding the two-track policy of pressure and engagement.”
Feb. 26 – The P5+1 held talks with Iran in Almaty, Kazakhstan.
March 14 - The U.S. Treasury Department sanctioned a Greek businessman and 14 companies for helping Iran evade international oil sanctions.
March 14 – The Pentagon reported that an Iranian fighter jet targeted a U.S. drone over the Gulf. No shots were fired and the jet left the area after a verbal warning.
March 18 – President Obama sent a fifth Nowruz message to Iran saying there could be a “new relationship” with Iran if it meets international obligations on its controversial nuclear program.
March 21 – Supreme Leader Ayatollah Ali Khamenei said he is not opposed to direct talks with the United States in a speech marking Nowruz. But he is “not optimistic” about prospects for success if negotiations take place. He also claimed that the United States “doesn’t want the nuclear conflict to end.”
June 3 – The United States imposed sanctions for the first time on Iran’s currency, the rial. The executive order’s objective was to render the currency unusable outside of Iran, a senior administration official said during a conference call.
June 4 – The United States sanctioned a major network of front companies for hiding assets on behalf of Iranian leaders.
June 18 – The Group of Eight industrialized nations called on Iran to move “without delay” to fulfill its long-delayed obligations in answering questions about its controversial nuclear program. It also called on the international community to fully implement a several U.N. sanctions resolutions designed to pressure Tehran into compliance.
July 1 – New U.S. sanctions banning gold sales and trade in gold with Iran went into effect.
Sept. 26 – Foreign ministers from P5+1 countries and Iran met on the sidelines of the U.N. General Assembly and agreed to hold a new round of talks in Geneva. Secretary of State John Kerry and Foreign Minister Mohammad Javad Zarif held their first meeting on the sidelines.
Sept. 27 – President Barack Obama called Iranian President Hassan Rouhani in what was the first direct communication between a U.S. and Iranian presidents since the 1979 revolution. “The two of us discussed our ongoing efforts to reach an agreement over Iran’s nuclear program,” Obama said at a White House briefing.
Oct. 15-16 – Diplomats from P5+1 countries and Iran met in Geneva to solve the nuclear dispute. They committed to meeting in November to continue talks that were “substantive and forward looking.”
Nov. 7-10 – Iran and the P5+1 made significant headway but ultimately failed to finalize an agreement. Foreign ministers rushed to Geneva as a breakthrough appeared imminent. But last-minute differences, reportedly spurred by French demands for tougher terms, blocked a deal.
Nov. 24 – Iran and the P5+1 reached an interim agreement that would significantly constrain Tehran’s nuclear program for six months in exchange for modest sanctions relief. Iran pledged to neutralize its stockpile of near-20 percent enriched uranium, halt enrichment above five percent and stop installing centrifuges. Tehran also committed to halt construction of the Arak heavy-water reactor.