Iran is marking the 40th anniversary of the 1979 Islamic revolution that ended the monarchy and heralded the start of four decades of clerical rule.

Hundreds of thousands of people were expected to attend government-orchestrated demonstrations in Tehran and other cities to commemorate February 11, 1979, when followers of Ayatollah Ruhollah Khomeini ousted a U.S.-backed monarch, Shah Reza Pahlavi.

In the capital, crowds were heading toward the central Azadi (Freedom) Square, where President Hassan Rohani was set to deliver a speech, as revolutionary and nationalist songs played over loudspeakers.

The festivities to mark the Iranian Revolution start every year on February 1, the day that Khomeini returned from exile to become supreme leader of the Islamic republic. They end on February 11, the day that the outgoing government collapsed.

Photo Gallery: In Pictures: Iran's 1979 Islamic Revolution

This years celebrations come amid heightened tensions with the United States, which last year withdrew from the 2015 nuclear agreement between Tehran and world powers and reimposed tough sanctions on the Iranian economy.

European signatories of the 2015 deal, under which Tehran pledged to curb its nuclear activities in exchange for sanctions relief, have been trying to save the accord.

In a February 8 speech to a gathering of Iranian Army Air Force officers, Irans Supreme Leader Ayatollah Ali Khamenei said that Iran will not give up the Death to America chant as long as Washington continues its hostile policies toward Tehran.

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Ahead of the celebrations, Iranian officials announced that up to 50,000 prisoners would either be released or have their sentences reduced.

According to official figures, nearly 250,000 people are incarcerated in Iran.

It was not clear whether the amnesty would also apply to political prisoners.

In a report coinciding with the celebrations, Reporters Without Borders (RSF) said that 61,900 political prisoners had been held in Iran since the 1980s.

Citing leaked Iranian Judiciary documents, the Paris-based media watchdog also said that the authorities had arrested, imprisoned, or executed at least 860 journalists in the three decades between the 1979 revolution and 2009.

With reporting by AP RFE/RL

RFE/RL journalists report the news in 25 countries where a free press is banned by the government or not fully established.

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