This year's anniversary comes as tensions rise with the United States and Iran grapples with the aftermath of President Donald Trump's pullout last May from the 2015 nuclear deal between Iran and world powers and tough USA economic sanctions, re-imposed in November.
Iran displayed its ballistic missile capabilities during a parade, including the Zolfaqar, a ground-to-ground missile with a 700 km (435 miles) range and the Qiam, with a range of 800 km, according to Tasnim news agency.
In capital Tehran, demonstrators marched across different routes to reach the Azadi (Liberty) Square, where President Hassan Rouhani gave an address.
"Our presence in the 40th anniversary of the revolution is to show our support for the Islamic Republic", said one sign held by a protester.
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.
An Iranian man marches with a portrait of the country's Supreme Leader Ali Khamenei (L) alongside a woman holding up another of Islamic Revolution founder Ayatollah Ruhollah Khomeini (R) during a ceremony celebrating the 40th anniversary of Islamic Revolution in the capital Tehran on February 11, 2019.
Iran even holds an annual "Death to America" rally every November to commemorate the seizure of the U.S. Embassy in 1979, leading to a 444-day hostage crisis in which the Iranian regime held 52 Americans prisoner.
"US should take note: REAL Iranians never succumb to diktats". "The enemies are now confessing to their defeat", said Rouhani.
But he remained defiant on Monday as Iranians recalled the end of a monarch who catered to the rich.
Yadollah Javani, the Iranian Revolutionary Guards' deputy head for political affairs, said Iran would demolish cities in Israel if the United States attacked.
"The United States does not have the courage to fire a single bullet at us despite all its defensive and military assets".
Israeli Prime Minister Benjamin Netanyahu fired back on Monday night after Iran threatened "to 'raze Tel Aviv and Haifa" to the ground, saying that if Tehran attacks Israel, it will be the last anniversary of the Islamic Revolution that they celebrate.
"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.
"If this regime makes the bad mistake of trying to destroy Tel Aviv and Haifa, it will not succeed", he said.
The cry of "Death to America" has long featured in the Islamic republic, with leaders and the public alike using it to vent their perception of America's supposed interest in working against the country. "They must leave the region", said Brig.
Today, the United States, its Arab allies and Israel are trying to counter Tehran's growing influence in the Middle East, where it has proxies in Syria, Lebanon and Yemen.
This is despite Mr Corbyn repeatedly saying there should be a general election if Mrs May can not get a deal through Parliament. But she said the Government is prepared to commit to asking Parliament if it wishes to follow suit if standards change.
As new data makes the more than four-billion mile journey to Earth, the Kuiper belt object's shape is coming into well, shape. Mission team members initially thought Ultima Thule resembles a snowman but now believe the object to be flattened.
Manager Pep Guardiola sank to his knees in frustration but he was soon celebrating as Aguero made amends in sensational fashion. The victory takes City clear of Liverpool on goal difference again, though Liverpool have a game in hand.
Abigail Arias has taken a solemn oath to continue to fight the bad guys. "Extremely tough, we cried for a few weeks". In December, Abigail met Garivey and told him about her dream to become a police officer.
The Make America Great Again rally will take place in El Paso , Texas on Monday at the County Coliseum. The president's rally comes four days before the nation could fall into another government shutdown.
At least 17 people were killed in the fire that broke out in Hotel Arpit Palace in Karol Bagh , Delhi earlier on Tuesday. Most of the victims - including many from a wedding party - were said to be sleeping when the fire broke out.
Iranian President Hassan Rouhani on Monday laid historical claims to a number of Arabian Gulf countries without naming them. In January, Mr Rouhani said Iran was facing its worst economic crisis since the Shah was toppled.
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