People take part in an anti-US protest in front of the former US mbassy in Tehran, Iran on November 4. Photo: IC

With anti-American slogans and effigies mocking US President Donald Trump, thousands rallied outside the former US embassy in Tehran on Monday to mark the 40th anniversary of the Iran hostage crisis.

Amid renewed tensions with the US, state television showed rallies taking place in several other cities four decades after revolutionary students stormed the diplomatic mission - an event that still strains ties today.

"They will continue their enmity against us. They are like a lethal scorpion whose nature is to have a poisonous sting," the head of the army, General Abdolrahim Mousavi, said in a speech in Tehran. "We are ready to crush this scorpion and will also pay the price."

He slammed the idea of interacting with the US as a ruse, echoing recent remarks by Iran's supreme leader Ayatollah Ali Khamenei.

Words like negotiation are a "gift wrapping... hiding the discourse of submission and defeat," Mousavi said, adding that the only way forward is "to maintain the revolutionary spirit through prudence and obeying the leader."

Replica missiles and the same type of air defense battery used to shoot down a US drone in June were put on display outside the former embassy-turned museum in Tehran.

Iranians massed in front of the building carrying placards with slogans such as "Down with USA" and "Death to America," according to AFP journalists at the scene.

Rallies were also reported in the cities of Mashhad, Shiraz and Esfahan, among others, with the Mehr News Agency estimating "millions of people" attended across the country, though it was not possible to verify that figure.

On November 4, 1979, less than nine months after the toppling of Iran's American-backed shah, students overran the embassy complex to demand the US hand over the ousted ruler after he was admitted to a US hospital.

It took 444 days for the ­crisis to end with the release of 52 Americans, but the US broke off diplomatic relations with Iran in 1980 and ties have been frozen ever since.