Hundreds of thousands of people gathered on the streets of the Iranian capital and cities around the country to mark the 35th anniversary of the Islamic Revolution.
In Tehran, huge crowds thronged central Azadi square on Tuesday for a speech by President Hassan Rouhani, his first major address to the public since his election in August.
Rouhani launched into the traditional anti-US rhetoric despite a significant political shift in Tehran, which resulted in his election last year as a leader pursuing a policy of outreach to the West.
"The people's vote had no role in running this country. This was a huge humiliation," Rouhani said, referring to the period when Iran was a constitutional monarchy.
"People wanted their views to be an influence [but] the big powers were interfering in the internal affairs of this country ... The Americans thought the country of Iran belongs to them. They interfered everywhere even on security issues."
The revolution was set in motion in 1979 after a siege began some 10 months following the fall of the US-allied shah.
Radical students stormed the US embassy, taking 52 people hostage. They were released after 444 days, and the seige ended Washington's diplomatic relations with Tehran.
More recently, Iran reached an interim agreement with Western powers to curb its nuclear programme, which the West suspects is meant to develop a nuclear bomb.
But while Tuesday's mood in Tehran is one of celebration, Al Jazeera's Soraya Lennie reported that Iranians still feel there is a lot that needs to be done to strengthen relations between the US and Iran.
"Yes, they want better relations with the United States, they're happy with the government and the diplomatic push from the government, but there's still so much anger in the people towards the history of Iran and the United States," Lennie said.
The slogan's of Tuesday's celebration express Iran's current feelings towards the US and include "we'll stand to the end", "we will stand up against and we are ready for all options on the table", and "we are ready for the great battle".
The first slogan is "obviously a reference to the United States and external pressures on Iran", Lennie said.
The second one is "of course a reference to President Obama, John Kerry and all options on the table including military ones", she said.
Lennie added that the third, like the first slogan, is also about external pressures on Iran.
Activities to mark the anniversary come a day after Iran "successfully tested" two missiles, according to the official IRNA news agency.
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Iran's ballistic missile programme has long been a source of concern for Western nations because it is capable of striking its arch-enemy Israel.
"The new generation of ballistic missile with a fragmentation warhead, and a Bina laser-guided surface-to-surface and air-to-surface missile, have been successfully tested," Hossein Dehgan, the defence minister, said.
He said the new ballistic missile could "evade anti-missile systems" and was capable of "great destruction".