Iran's supreme leader has slammed "thugs" who attacked public property during rare anti-regime demonstrations across the country.

Key points: Tens of thousands have taken to the streets, some destroying petrol stations

Tens of thousands have taken to the streets, some destroying petrol stations Iran has imposed its "largest-ever" internet shutdown

Iran has imposed its "largest-ever" internet shutdown The US Government has condemned violence against protesters

The Government shut down internet access across the nation of 80 million people to staunch protests that took place in a reported 100 cities and towns.

The move made it increasingly difficult to gauge whether unrest continued, with internet firm Oracle calling it "the largest internet shutdown ever observed in Iran".

Protests erupted days ago over authorities' decision to increase petrol prices by more than 50 per cent.

Local media showed the scale of the damage in images published of burned gas stations and banks, torched vehicles and roadways littered with debris.

The White House said Iran's ruling class had abandoned its people. ( AP: Morteza Zangane via ISNA )

Since the price hike, demonstrators have abandoned cars along major highways and joined mass protests in the capital, Tehran, and elsewhere.

Supreme leader Ayatollah Ali Khamenei said "some lost their lives and some places were destroyed," without elaborating.

He called the protesters "thugs" who had been pushed into violence by counter-revolutionaries and foreign enemies of Iran.

Ayatolla Ali Khamenei has urged security forces to "implement their tasks". ( AP: Office of the Iranian Supreme Leader )

Mr Khamenei specifically named those aligned with the family of Iran's late shah, ousted 40 years ago, and an exile group called the Mujahedeen-e-Khalq (MEK).

The MEK calls for the overthrow of Iran's Government and enjoys the support of President Donald Trump's personal lawyer, Rudy Giuliani.

"Setting a bank on fire is not an act done by the people. This is what thugs do," Mr Khamenei said.

Authorities said some 100 banks and other stores were looted and vandalised. ( AFP )

Several dead as violence breaks out

In some cities protests turned violent, with demonstrators setting fires as gunfire rang out.

It remains to be seen how many people were arrested, injured or killed.

Videos from the protests have shown people gravely wounded. Iranian authorities have raised the official death toll in the violence to at least three.

Attackers targeting a police station in the western city of Kermanshah on Saturday killed an officer, the state-run IRNA news agency reported.

A government official said another person was killed in a suburb of Tehran. Meanwhile, one man was reported killed on Friday in Sirjan, around 800 kilometres south-east of Tehran.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 45 seconds 45 s Protests over shock fuel price hikes in Iran kills one person

Mr Khamenei ordered security forces "to implement their tasks" and for Iran's citizens to keep clear of violent demonstrators.

Iran's Intelligence Ministry said the "key perpetrators of the past two days' riot have been identified and proper action is ongoing" — seeming to indicate a crackdown could be looming.

Economic protests in late 2017 into 2018, as well as those surrounding its disputed 2009 presidential election, were met with a heavy reaction by the police and the Basij, the all-volunteer force of Iran's paramilitary Revolutionary Guard.

A man walks past a fire set by protesters in Abadan, Iran. ( AP: IRIB )

The semi-official Fars news agency, close to the Guard, put the total number of protesters at over 87,000, saying demonstrators ransacked some 100 banks and stores in the country.

Authorities arrested some 1,000 people, Fars reported, citing unnamed security officials for the information.

Trump administration criticises Iranian response

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The protests have put renewed pressure on Iran's Government as it struggles to overcome the US sanctions that have strangled the economy since Mr Trump unilaterally withdrew America from the nuclear deal over a year ago.

While representing a political risk for President Hassan Rouhani ahead of February parliamentary elections, the demonstrations also show widespread anger among the Iranian people, who have seen their savings evaporate amid scarce jobs and the collapse of the national currency, the rial.

Cheap petrol is practically considered a birthright in Iran, home to the world's fourth-largest crude oil reserves despite decades of economic woes since its 1979 Islamic Revolution.

In a statement issued on Sunday, the Trump administration condemned "the lethal force and severe communications restrictions used against demonstrators".

"Tehran has fanatically pursued nuclear weapons and missile programs, and supported terrorism, turning a proud nation into another cautionary tale of what happens when a ruling class abandons its people and embarks on a crusade for personal power and riches," the White House statement said.