TEHERAN (AFP) - Thousands of Iranians gathered in central Teheran on Monday (Feb 11) to mark 40 years since the Islamic revolution, a political earthquake that ended millennia of monarchy and still reverberates around the region.

Traffic was diverted from roads leading up to Azadi (freedom) Square ahead of a march to remember the day in 1979 when Ayatollah Ruhollah Khomeini ousted the shah's last government.

Stalls set up by state institutions handed out tea and cakes, and choirs sang revolutionary songs as crowds massed despite driving rain.

Life-size replicas of Iranian-made cruise and ballistic missiles lined the route in a statement of defiance at a time of heightened tensions with the United States.

The event on Monday is the culmination of official celebrations called the 10 Day Dawn that mark the period between Feb 1 and Feb 11, 1979, when the revolution's leader Khomeini returned from exile and toppled the monarchy.

The state has played up this year's anniversary, as 40 is symbolic of maturity in the Islamic tradition and the age at which Prophet Muhammad received revelations from God.

But despite the official festivities, today's Islamic republic faces acute economic challenges, as it struggles with a mix of domestic hardships and United States sanctions.

Extensive fireworks displays were held across Teheran on Sunday night.

Before the fireworks, supporters of the revolution shouted chants of "Allahu Akbar" (God is greatest) from rooftops, recalling the protests that swept Khomeini to power four decades earlier.

Current supreme leader Ayatollah Ali Khamenei is set to publish "a detailed statement explaining the 'second step' of the progress of the Islamic revolution", his official website said.