In this February 11, 2016 file photograph, an Iranian woman holds the national flag during a rally commemorating the 37th anniversary of the Islamic revolution, in Tehran, Iran.
State TV showed crowds defying rainy weather and carrying Iranian flags while shouting anti-Israeli and anti-US slogans.
On Feb 11, 1979, Iran's army declared its neutrality, paving the way for the collapse of the Shah Mohammad Reza Pahlavi, the United States's closest ally in the Middle East.
Iran's president also insisted that Iranians "have not asked and will not ask for permission" to develop different types of missiles, Rohani said.
Life-size replicas of Iranian-made cruise and ballistic missiles stood in a statement of defiance after the USA previous year reimposed sanctions following its withdrawal from a deal on Tehran´s nuclear programme.
The large turnout in state-sponsored rallies, in which USA and Israeli flags were burned, came as Iranians face mounting economic hardships which many blame on the country's clerical leaders.
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The large turnout in state-sponsored rallies came as Iranians face mounting economic hardships following the return of USA sanctions a year ago.
"Much to the dismay of America, the revolution has reached its 40th year", read one banner.
"I don't ignore the threats from the Iranian regime, but I'm also not intimidated by them", Netanyahu said in a Hebrew-language video.
U.S. President Donald Trump tweeted on Monday that the Iranian government had let down its people. Prime Minister Benjamin Netanyahu took note and responded: try it, and it will be the last Revolution Day the Iranians will ever celebrate.
Washington and its Arab allies have viewed Iran with great suspicion since the Islamic Revolution, fearing Khomeini's radical ideology would inspire militants across the Middle East.
"The presence of people in this celebration means that plots by the enemies ... have been defused", Rouhani said.
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Iranians march towards Azadi Square during Monday's rally.
"They must leave the region", Brigadier General Hossein Salami said.
Javani, the deputy for the IRGC political bureau, was speaking at a rally marking the 40th anniversary of the Islamic Revolution, when the US-backed monarchy was overthrown and replaced in power by Islamic fundamentalists.
Soldiers, students, clerics and black-clad women holding small children flocked to the streets of cities and towns, many carrying portraits of Khomeini and Iran's current supreme leader, Ayatollah Ali Khamenei.
An anchor on state television warned of hostile foreign media trying to downplay the participation of Iranians in the march but expressed confidence that "they would be confounded by the unprecedented level of attendance".
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