FACTBOX: Iranian students' 1979 storming of U.S. embassy

(Reuters) - Police clashed with supporters of Iran's opposition leader Mirhossein Mousavi in Tehran on Wednesday when a rally marking the 30th anniversary of the storming of the U.S. embassy turned violent, witnesses said.

Here are some key facts on events leading up to and after the 1979 storming of the U.S. embassy in Tehran by radical Iranian students.

* Students helped spearhead the ousting of the U.S.-backed Shah, Mohammad Reza Pahlavi, in the 1979 Islamic revolution. Rioting throughout late 1978 induced the Shah to leave Iran in January 1979. The Shah, who was already gravely ill, sought refuge in Morocco, Mexico and the United States. Exiled cleric Ayatollah Ruhollah Khomeini returned to Iran in triumph to seal victory for a revolution whose mantra was "Death to America."

* Iranian student activists in coordination with radical clerics stormed the U.S. embassy in Tehran, taking 90 hostages. Fifty-two were held captive for 444 days with the students demanding the extradition of the deposed Shah from the United States.

* The siege prompted then U.S. President Jimmy Carter to freeze Iranian assets and sever all diplomatic ties with Tehran.

* On April 25, 1980, a U.S. commando mission to rescue the hostages was abandoned in the desert with the loss of eight American lives when a helicopter collided with a tanker aircraft, politically damaging President Carter.

* Iran freed the hostages to coincide with the inauguration of Carter's rival Ronald Reagan on January 20, 1981.

* The deposed Shah died in exile in Egypt in July 1980.

* Ayatollah Khomeini, the founding father of the 1979 Islamic revolution, was reported to be initially unsure about the students' action but changed his mind when he saw the crowds of demonstrators gathering in front of the embassy compound to voice their support for the takeover.

-- He hailed the students for launching "a second revolution, greater than the first."