Protesters rallied across Iran and strikes were reported throughout the country's Kurdish region on Saturday as demonstrations against the death of a woman in police custody entered their third week.

The protests, sparked by the death of Mahsa Amini, a 22-year-old from Iranian Kurdistan, have spiralled into the biggest show of opposition to Iran's clerical authorities since 2019, with dozens killed in unrest across the country.

People demonstrated in London and Paris and elsewhere on Saturday in solidarity with Iranian protesters, some holding pictures of Amini, who died three days after being arrested by the Islamic Republic's morality police for "unsuitable attire".

In Iran, social media posts showed rallies in large cities including Tehran, Isfahan, Rasht and Shiraz.

In Tehran's traditional business district of Bazaar, anti-government protesters chanted "We will be killed one by one if we don't unite", while elsewhere they blocked a main road with a fence torn from the central reservation, videos shared by the widely followed Tavsir1500 Twitter account showed.

Students also demonstrated at numerous universities. At Tehran University, dozens were detained, Tavsir1500 said. The semi-official Fars news agency said some protesters were arrested in a square near the university.

Tavsir1500 also posted what it said was a video taken at the gates of Isfahan University during which shots could be heard. A separate video showed tear gas being fired at the university, dispersing a group of people.

The protests began at Amini's funeral on September 17 and spread to Iran's 31 provinces, with all layers of society, including ethnic and religious minorities, taking part and many demanding Supreme Leader Ayatollah Ali Khamenei's downfall.

Amnesty International has said a government crackdown on demonstrations has so far led to the deaths of at least 52 people, with hundreds injured. Rights groups say dozens of activists, students and artists have been detained.

In London, about 2,500 people staged a noisy protest in Trafalgar Square. Few women among the mostly Iranian crowd agreed to be interviewed on camera, fearful of identification and reprisals by the authorities.

In central Paris, a crowd of several dozen people gathered to show support for Iranian protesters, holding Iranian flags and pictures of victims who have died in the protests.

Iranian authorities say many members of the security forces have been killed, accusing the United States of exploiting the unrest to try to destabilise Iran.

The Revolutionary Guards said four members of its forces and the volunteer Basij militia were killed on Friday in attacks in Zahedan, capital of the southeastern Sistan-Baluchistan province. (Reuters)