TMELINE-U.S.-Iran relations

(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 November 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.