At least 12 people have been killed and multiple others wounded during a fourth night of unrest in Iran.

Iranian state TV reported the figure Monday, saying security forces repelled 'armed protesters' who tried to take over police stations and military bases.

Two people were shot dead in the southwestern town of Izeh while another two died in Dorud after being run over by a stolen fire truck, local news agencies reported.

Elsewhere there were unconfirmed reports that three people were shot dead after security forces opened fire on protesters in Isfahan.

Twelve people have been reported dead during a fourth straight night of protests in Iran, including reports of three people killed in the city of Isfahan

Video purportedly taken in Isfahan on Sunday night shows dozens of people on the street before what sounds like gunshots are heard

Video purportedly filmed in the city shows dozens of marchers on the streets as vehicles burn around them before what sounds like gunshots are heard.

The deaths in Izeh were confirmed by local politician Hedayatollah Khademi, who said it was unclear whether they were killed by police or other demonstrators.

'The governor said it (the gunfire) was unlikely to be by police as they were not supposed to open fire,' he said.

The shooting in Isfahan was reported by several prominent Twitter personalities including Amichai Stein, foreign affairs correspondent for the Israeli public broadcasting corporation, but could not be independently verified.

Elsewhere police used tear gas and water cannon to disperse a small protest in Tehran's Enghelab Square on Sunday evening.

Protesters in the small northwestern town of Takestan torched a school for clergy and government buildings, the ILNA news agency said, while the state broadcaster said two people had died in Dorud after crashing a stolen fire engine.

There were also reports of protests in the cities of Izeh (southwest), Kermanshah and Khorramabad (west), Shahinshahr (northwest) and Zanjan (north).

Verifying reports remained challenging due to travel restrictions and sporadic blocks on mobile Internet and popular social media sites including Telegram and Instagram.

The protests began as demonstrations against economic conditions in second city Mashhad on Thursday but quickly turned against the Islamic regime as a whole, with thousands marching in towns across Iran to chants of 'Death to the dictator'.

'The people are absolutely free in expressing their criticisms and even protests,' Rouhani said in a message on the state broadcaster.

Crowds continued to gather in Iran despite the government blacking out the Telegram messaging app and Instagram

Police have used water cannon to disperse protesters who had gathered in Ferdowsi Square, Tehran

'But criticism is different to violence and destroying public property.'

He sought a conciliatory tone, saying that government bodies 'should provide space for legal criticism and protest' and calling for greater transparency and a more balanced media.

US President Donald Trump said the 'big protests' showed people 'were getting wise as to how their money and wealth is being stolen and squandered on terrorism'.

'Looks like they will not take it any longer,' he wrote on Twitter.

In a later tweet, Trump accused Iran of 'numerous violations of human rights,' and commented on the disruption to social media, saying it 'has now closed down the Internet so that peaceful demonstrators cannot communicate. Not good!'

Rouhani dismissed Trump's comments.

'This man who today in America wants to sympathise with our people has forgotten that a few months ago he called the nation of Iran terrorist.

'This person whose whole being is against the nation of Iran has no right to feel pity for the people of Iran.'

Hassan Rouhani said people were 'completely free to express their criticism' of the government but violence would not be tolerated in his first public remarks on the crisis

Protests started in the north east city of Mashhad last week but have since spread around the country in the most serious challenge to the regime since 2009

After initial silence, state media began showing some footage on Sunday, focusing on young men attacking banks and vehicles, an attack on a town hall in Tehran, and images of a man burning the Iranian flag.

Two hundred people were reported to have been arrested in Saturday night's unrest in the capital.

'Those who damage public property, disrupt order and break the law must be responsible for their behaviour and pay the price,' Interior Minister Abdolrahman Rahmani Fazli said on Sunday.

'The spreading of violence, fear and terror will definitely be confronted,' he added.

There have been reminders of the continued support for the regime among conservative sections of society, with pro-regime students staging sizeable counterdemonstrations at the University of Tehran over the weekend.

Rouhani came to power in 2013 promising to mend the economy and ease social tensions, but anger over high living costs and a 12-percent unemployment rate have left many feeling that progress is too slow.

President Trump continued his attacks on the Iranian regime via Twitter as Rouhani said he has 'no right to feel pity for the people of Iran'

Unemployment is particularly high among young people, who are generally considered less deferential to authority.

'Rouhani has run an austerity budget since 2013 with the idea that it's a tough but necessary pill to swallow to manage inflation and currency problems and try to improve Iran's attractiveness for investment,' said Esfandyar Batmanghelidj, founder of the Europe-Iran Forum.

'But choosing years of austerity immediately after a very tough period of sanctions is bound to test people's patience,' he told AFP.

Police have so far taken a relatively soft approach to the unrest. They deny shooting two men killed in Dorud on Saturday night, although information has been hard to obtain amid the near-total media blackout.

The authorities have blamed external forces for fomenting violence, saying the majority of social media reports were emanating from regional rival Saudi Arabia or exile groups based in Europe.

Since the ruthless repression of the 2009 protests against a disputed presidential election that gave hardliner Mahmoud Ahmadinejad a second term, many middle-class Iranians have abandoned hope of securing change from the streets.

But low-level strikes and demonstrations have continued, with groups such as bus drivers, teachers and factory workers regularly protesting against unpaid wages and poor conditions.