Iran's Supreme Leader has blamed foreign "enemies" for anti-government protests that have left more than 20 people dead, in his first public reaction to escalating demonstrations.

Key points: Secretary of Iran's Supreme National Security Council blames US, Britain, Saudi Arabia for protests

Secretary of Iran's Supreme National Security Council blames US, Britain, Saudi Arabia for protests Iranian police have reportedly arrested 450 protesters in Tehran over the past three days

Iranian police have reportedly arrested 450 protesters in Tehran over the past three days Authorities warn protesters they could face the death penalty

Security forces have struggled to contain protests that broke out last Thursday and have continued nationwide in the boldest challenge to the country's clerical leadership in years.

Iranian state television said on Tuesday nine people, including at least two members of the security forces, had died overnight during protests in one province alone.

And in a sign of potential escalation, a local governor said six of the dead were killed in an attack on a police station.

Supreme Leader Ayatollah Ali Khamenei accused foreign "enemies" of fuelling the protests.

"In recent days, enemies of Iran used different tools including cash, weapons, politics and intelligence apparatus to create troubles for the Islamic Republic," he said.

Sorry, this video has expired What's fuelling the deadly protests in Iran? (Photo: AP)

He did not mention any enemies by name but Ali Shamkhani, secretary of the Supreme National Security Council, said the United States, Britain and Saudi Arabia were behind the recent riots in Iran.

"Saudis will receive Iran's unexpected response and they know how serious it can be," Mr Shamkhani was quoted as saying by Tasnim news in an interview with Beirut-based Al Mayadeen TV.

Iranian police have arrested 450 protesters in Tehran over the past three days, the ILNA news agency quoted Ali Asghar Nasserbakht, a security deputy governor of Tehran, as saying.

Mr Nasserbakht said 200 protesters were arrested on Saturday, 150 on Sunday and 100 on Monday.

He said the situation in Tehran was under control and the police had not asked for the help of the Revolutionary Guards special forces.

Protesters warned they could face death penalty

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The unrest began in Iran's second largest city, Mashhad, in the form of protests against price rises, but swiftly spread and took a more political tone.

Iran is a major OPEC oil producer and regional power but frustrations have grown at home as the country's economy struggles.

Protesters have also expressed anger over Iran's involvement in the wars in Syria and Iraq.

Sorry, this video has expired Iran State TV coverage of protests (Photo: AP)

The head of Iran's Revolutionary Court has warned arrested protesters could potentially face the death penalty when they come to trial.

State TV said six rioters were killed during an attack on a police station in the town of Qahdarijan. It said those clashes were sparked by rioters who tried to steal guns from the police station.

The unrest is the worst since crowds took to the streets in 2009 to condemn the re-election of then-president Mahmoud Ahmadinejad.

'Trump should focus on America'

Iranian state television reported that nine people have been killed in the latest night of protests ( AP )

President Hassan Rouhani on Monday refrained from accepting responsibility for the problems raised by protesters, blaming his predecessor and Iran's long-time adversary the United States for the problems.

Mr Rouhani, seen as a pragmatist who is at odds with hardliners, said: "People on the streets do not ask for bread and water, but for more freedom."

The remark implied that the protesters were not targeting his government, but the more rigid clerical establishment.

US President Donald Trump, a critic of the Iranian regime, has tweeted daily in support of the protesters.

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Iranian Foreign Ministry spokesman Bahram Qasemi said: "Instead of wasting his time by publishing offensive tweets to other nations, Trump should focus on internal affairs of America."

A US official who is following developments told Reuters Mr Trump's tweets were playing into the Iran Government's hands and allowing it to accuse enemies of the Islamic Republic of fomenting the unrest.

"What the President is doing is taking the focus off the real reasons for the protests, like the foreign adventures and the corruption, and putting it on himself," said the US official, who spoke on the condition of anonymity.

The source added US intelligence officials thought the protesters had little chance of toppling the Government.

Turkey said it was concerned by reports of people dying and public buildings being damaged, while France said it was concerned by the number of victims and arrests.

Sorry, this video has expired Deaths reported during anti-Government protest in Iran

The Russian Foreign Ministry was quoted by the RIA news agency as saying external interference was destabilising the situation, and calling it "unacceptable".

Iran and Russia are the main allies of Syrian President Bashar al-Assad, while the United States, Saudi Arabia and Turkey support rebel groups.

Meanwhile, Syria criticised the US and Israel for expressing support for the protesters in Iran, and accused the two nations of destablising the region.

Its foreign ministry said no-one should interfere in Iran's internal affairs, adding that Syria was confident Iran's leadership, government and people would be able to defeat the "conspiracy".

ABC, wires