"The presence of people today on the streets all over Islamic Iran... means that the enemy will never reach its evil objectives," a defiant President Hassan Rouhani told those thronging Tehran's Azadi (Freedom) Square Monday, decrying a "conspiracy" involving Washington.
Chador-clad women, militia members in camouflage fatigues and ordinary citizens marched through the capital in freezing rain to commemorate the day in February 1979 that Ayatollah Ruhollah Khomeini ended millennia of royal rule.
The routes leading up to the square were packed with people as loudspeakers blared revolutionary anthems and slogans.
Life-size replicas of Iranian-made cruise and ballistic missiles stood in a statement of defiance after the US last year reimposed sanctions following its withdrawal from a deal on Tehran's nuclear programme.
"We have not, and will not, request permission from anyone for increasing our defensive power and for building all kinds of... missiles," he told the crowd.
"Today the whole world should know that the Islamic Republic of Iran is considerably more powerful than the days of the war," Rouhani said.
Seemingly reaching out to his political critics within the country, the president added: "The more we allow different ideas, beliefs and (political) factions the stronger our system will be."
A pre-prepared resolution was read out ahead of his speech that proclaimed "unquestioning obedience to the supreme leader Ayatollah Ali Khamenei" and called US President Donald Trump an "idiot".
Trump's chief foreign policy adviser said on Monday the Islamic revolution inflicted four decades of "failure and broken promises" on the country.
The events Monday were the culmination of official celebrations called the "10 Day Dawn" that marks the period between February 1, 1979 and February 11 when Shiite cleric Khomeini returned from exile and ousted the shah's last government.
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.
But despite the official festivities today's Islamic republic faces acute economic challenges as it struggles with a mix of domestic hardships and US sanctions.
Banners held by marchers or hung along the streets bore slogans including "Death to America", "Death to Israel", "we will trample on America", "forty yeas of challenge, forty years of US defeats".
A number of Israeli and American flags were set on fire by the crowds. An anchor on state television warned of hostile foreign media trying to downsize the participation of Iranians in the march but expressed confidence that "they would be confounded by the unprecedented level of attendance".
Those who took to the streets were bullish despite the economic problems in the country, made worse by Washington's punitive measures. Former public servant Saaghi insisted that it remained paramount for Iranians to stick by the revolution.
"We are here to support the revolution," the 57-year-old pensioner, who refused to give his first name, told AFP at the event in Tehran.
He compared the US sanctions and economic hardships to "riding a bicycle when someone puts a stick in the wheels" but pointed to advances in other fields as more than making up for them.
"On the revolution's 40th anniversary we are at the top for scientific achievements like nanotechnology or accurate missiles," he said.
"Iran has changed from a backward nation to a world power," said the 50-year-old.
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