A videos posted on social media appeared to show two young Iranian men lying motionless on the ground and covered with blood and a voiceover said they had been shot dead by police.

It claimed security forces fired on protesters in the western town of Dorud and killed at least two as other protesters in the same video were chanting, 'I will kill whoever killed my brother!'.

Other videos showed protesters setting fire to a government office in the city of Khorramabad while in the capital Tehran, demonstrators were filmed tearing down a picture of Supreme Leader Ayatollah Ali Khamenei.

A video appeared to show the bodies of two protesters who it was claimed had been shot dead by protesters in the city of Dorud

Protesters set fire to a government office in the city of Khorramabad as the protests continued into the night

Demonstrators burnt cars in Tehran after violent clashes earlier in the day at the city's university

Demonstrators attacked a town hall in Tehran as protests spilled into a third night despite government warnings against any further 'illegal gatherings' and moves to cut off the internet on mobiles.

After a day of clashes between rock throwing protesters and riot police, who responded with tear gas, at Tehran University, the demonstrations continued after dark and spread across the country.

There was chaos earlier around the capital's university as hundreds took to the streets, blocking traffic and shouting slogans against the regime.

Travel restrictions and a near-total media blackout from official agencies, made it difficult to confirm the reports.

The demonstrations appear to be the largest to strike the Islamic Republic since the protests that followed the country's disputed 2009 presidential election.

Thousands already have taken to the streets of cities across Iran, beginning at first on Thursday in Mashhad, the country's second-largest city and a holy site for Shiite pilgrims.

A large crowd took to the streets of Tehran to protest against the government for a third day

A crowd tore down a banner depicting the Supreme Leader Ayatollah Ali Khamenei

Ayatollah Ali Khamenei has been the focus for much of the Iranian protesters anger

The demonstrations are the largest in Iran since those that took place after the disputed presidential election of 2009

Protesters set fire to a police motorbike in the city of Mashhad, in the north-east of Iran

Donald Trump tweeted his support for the protesters in Iran saying 'oppressive regimes cannot endure for ever'

But the authorities could also count on a show of strength, with hundreds of counter-demonstrators seizing control of the university entrance, chanting 'Death to the seditionists'.

The authorities were also fortunate that annual rallies marking the defeat of the 2009 protest movement had already been scheduled for Saturday morning and brought thousands of regime supporters to the streets across the country.

The rallies, scheduled weeks earlier, commemorated a challenging those who rejected the re-election of hard-line President Mahmoud Ahmadinejad amid fraud allegations.

US President Donald Trump posted on Twitter two clips of his speech to the UN General Assembly in September in which he took aim at the Iranian regime, which Washington has held out as its top adversary in the Middle East.

'Oppressive regimes cannot endure forever, and the day will come when the Iranian people will face a choice. The world is watching!' he tweeted, quoting from the speech.