Jan 7 (Reuters) - Five Iranian boats carried out aggressive manoeuvres and showed hostile intent against three U.S. Navy ships at the weekend in the Strait of Hormuz, the Pentagon said on Monday, an incident Iran played down as "ordinary". The two have not had formal diplomatic relations for more than 25 years.

Following is a chronology of major events in bilateral relations.

1953 - CIA helps orchestrate overthrow of Iran's popular Prime Minister Mohammed Mossadegh, restoring to power the Shah, Mohammed Reza Pahlavi.

1979 - Revolt forces U.S.-backed Shah to flee, Ayatollah Ruhollah Khomeini returns from exile and becomes supreme religious guide. Fundamentalist students demanding Washington hand over the Shah for trial seize U.S. embassy in Tehran on Nov. 4 and hold staff hostage for 444 days.

1980 - United States cuts ties with Tehran, seizes Iranian assets and bans most trade with Iran. Covert U.S. rescue attempt ordered by President Jimmy Carter fails when helicopter crashes in sandstorm and eight U.S. servicemen are killed.

1981 - Iran releases U.S. hostages minutes after Carter steps down and Ronald Reagan is inaugurated as U.S. president.

1986 - Reagan reveals secret arms deal with Tehran in violation of U.S. arms embargo. Money from the sales was secretly passed to Contra guerrillas in Nicaragua.

1988 - U.S. warship Vincennes mistakenly shoots down Iranian passenger plane over the Gulf, killing all 290 aboard.

1995 - President Bill Clinton issues executive orders preventing U.S. companies from investing in Iranian oil and gas and trading with Iran. U.S. accuses Iran of supporting terrorism and trying to acquire nuclear weapons. Iran denies the charges.

2002 - President George W. Bush declares Iran, Iraq, North Korea an "axis of evil." U.S. accuses Tehran of operating secret nuclear weapons programme. Russia continues work on Iran's long-delayed first nuclear power plant, started under the Shah.

2006 - Washington says willing to join multilateral talks with Iran if it verifiably suspends nuclear enrichment. U.N. Security Council passes resolution imposing trade sanctions on Iran's sensitive nuclear materials and freezing assets of Iranian individuals and companies linked to the program.

2007

February - Iran denies U.S. accusations it is stoking violence in Iraq by supplying militants with weapons.

-- U.N. Security Council passes resolution imposing new financial and arms sanctions on Iran for refusing to suspend its nuclear program.

April - Ahmadinejad says Iran could reconsider its relations with the United States if Bush administration changes behaviour.

May - Iranian Foreign Minister Manouchehr Mottaki and U.S. Secretary of State Condoleezza Rice chat briefly on the sidelines of conference in Egypt.

U.S. urges Iran to stop supporting militias in Iraq when their ambassadors meet in Baghdad, highest-profile meeting in almost 30 years.

September - President Ahmadinejad says in U.S. TV interview that Iran does not need nuclear weapons, is not heading for war with United States.

October - Iran says it will help the U.S. stabilise Iraq if Washington sets out a troop withdrawal timetable.

-- U.S. military commander General David Petraeus accuses Iran of stoking violence in Iraq, says Iranian ambassador to Baghdad is member of Revolutionary Guards Qods force.

-- U.S. says Iran's Revolutionary Guards are a proliferator of weapons of mass destruction and its elite Qods force a supporter of terrorism.

December - Iran welcomes U.S. intelligence report that Iran ended its nuclear weapons program, says its aims are peaceful. Head of U.N. nuclear watchdog says report "somewhat vindicates" Iranian position.

January 2008 - Five Iranian boats carry out aggressive manoeuvres, show hostile intent against three U.S. Navy ships in the Strait of Hormuz. Iran plays down the incident. (Writing by David Cutler; Editing by Tim Pearce)

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