Iranian state television aired a video apparently showing that calm had returned to Tehran's Evin prison on Sunday after a fire broke out there overnight, as unrest sparked by Mahsa Amini's death in police custody last month.

Iranian authorities said the workshop had been set on fire "after a fight among a number of prisoners convicted of financial crimes and theft". Evin holds many detainees facing security charges, including Iranians with dual nationality.

Asked about the prison fire, U.S. President Joe Biden told reporters during a campaign trip on Saturday to Portland, Oregon that the Iranian government was "so oppressive" and that he was surprised by the courage of the Iranian protesters.

Iran's foreign ministry said Biden had interfered in state matters by showing support for the anti-government protests. The authorities have responded with a brutal crackdown.

Rights groups said at least 240 protesters had been killed in the anti-government protests, including 32 minors. Over 8,000 people had been arrested in 111 cities and towns, Iranian activist news agency HRANA said on Saturday.

Among the casualties have been teenage girls whose deaths have become a rallying cry for more demonstrations across the country.

Iran, which has blamed the violence on enemies at home and abroad, deny security forces have killed protesters. State media said on Saturday at least 26 members of the security forces had been killed by "rioters".

The protests have attracted international condemnation, with the United States, Canada and some European countries imposing sanctions on Iranian officials and organisations "involved in the clampdown on protesters".

"On Saturday ... Biden interfered in Iran's state matters by supporting the riots ... In recent days, the U.S. administration has tried desperately to inflame unrest in Iran under various excuses," Foreign Ministry spokesman Nasser Kanaani said, ISNA reported.

The footage of Evin aired on state television showed firefighters inspecting a workshop with fire damage to the roof. It also showed inmates in their wards apparently "sleeping as calm has been restored".

State news agency IRNA said on Saturday eight people were injured in the fire at the Evin prison. But the semi-official Fars news agency reported on Sunday that "no exact official figure of those injured or possible casualties have been published yet".

Video obtained by Reuters showed protesters marching amongst traffic towards Tehran's Evin prison on Saturday night and into Sunday morning.

Iran's notorious Evin prison, which holds criminal convicts as well as political detainees, has long been criticised by Western rights groups and was blacklisted by the U.S. government in 2018 for "serious human rights abuses".

The protests mark one of the boldest challenges to clerical rule since the 1979 revolution, with demonstrations spreading across the country and widespread calls for the downfall the Islamic Republic, even if the unrest does not seem close to toppling the system. 

Reuters