Iranian President Hassan Rouhani told Iranians who had gathered in Tehran's Azadi (Freedom) Square they should resist a "conspiracy" involving Washington.
On 11 February 1979, Ayatollah Ruhollah Khomenei came to power in Iran, replacing Shah Mohammad-Reza Pahlavi's Western-backed government, turning the country into an Islamic Republic. Loudspeakers are blaring out revolutionary and nationalist songs to encourage people to join the rallies.
This year's anniversary comes as Iran deals with the aftermath of President Trump's decision in May to withdraw from the 2015 nuclear deal and restore tough USA sanctions.
Iran displayed its ballistic missile capabilities during Tehran rally, parading two missiles capable of reaching up to 800 kilometres.
Since the revolution, Iran has become more divided. "We are doing everything necessary", he concluded.
Ayatollah Khamenei recently said when they chant "death to America" they really just mean death to President Donald Trump and his Cabinet.
Iranian state TV anchor Mehdi Khosravi chirped how he expects John Bolton, U.S. national security adviser, to be very angry on Monday since he had once predicted that Iranians will not see the 40th anniversary of their revolution.
"40 years of corruption".
The hardliners, who believe in the strict implementation of laws from 40 years ago, continuously clash with the reformists, who are pushing for more economic transparency. 40 years of terror.
"We do not and we will not ask permission for producing any type of missiles from anybody", Rouhani said in his speech Monday, though he stressed that Iran would "continue constructive engagement" with the global community. "The long-suffering Iranian people deserve a much brighter future", he posted in both English and Farsi.
Israeli Prime Minister Benjamin Netanyahu confirmed on Tuesday that Israel had carried out an artillery attack in Syria on Monday night.
Hakeem Al Araibi boards plane leaving Thailand for Australia
Before his departure she said she wanted him to get on the plane before she could believe he was being released. He had been playing for a semi-professional soccer team in Melbourne before he was detained in Thailand .
"If this regime makes the very bad mistake of trying to destroy Tel Aviv and Haifa, it will not succeed", the Israeli leader said. "However, this would be the last anniversary of the revolution that they celebrate".
Hundreds of thousands of Iranians marched and some burned U.S. flags to mark the revolution as Tehran showed off ballistic missiles in defiance of USA efforts to curb its military power.
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 Mohammed received revelations from God.
The US officially removed MEK, which describes itself as the biggest rival to the ruling Islamic Republic authorities, from its terrorism blacklist in 2012.
Gen. Qassem Soleimani, the head of Iran's elite Quds Force, attended a rally in the southern city of Kerman.
Some of the protesters burned USA flags.
A number of Israeli and American flags were set on fire by the crowds.
Former public servant Saaghi insisted that it remained paramount for Iranians to stick by the revolution. "And that's why, before 2019, we here will celebrate in Tehran!" he claimed. Trump also reestablished USA economic sanctions against Iran.
Fakheri, who was one of the revolutionaries on the streets of Tehran in 1979, said she would defend the revolution all over again.
"Iran has changed from a backward nation to a world power", said the 50-year-old.