Iran's Supreme Leader has blamed country-wide protests on "enemies of Iran" as the death toll from anti-government demonstrations rose to 22.
The demonstrations, the largest to strike Iran since its disputed 2009 presidential election, have brought six days of unrest across the country.
Around 450 protesters have been arrested in the capital Tehran over the last three days, the semi-official ILNA news agency reported.
The agency quoted Ali Asghar Nasserbakht, a security deputy governor of Tehran, who said 200 protesters were arrested on Saturday, 150 on Sunday and 100 were arrested Monday.
Offering his first comments since the protests began, Supreme Leader Ayatollah Ali Khamenei accused the "enemies of Iran" of meddling in the country's affairs.
"In the recent days' incidents, enemies of Iran utilized various means — including money, weapons, politics and intelligence apparatuses — to create problems for the Islamic system," he said.
The protests began on Thursday in Mashhad over Iran's weak economy and a jump in food prices and have expanded to several cities, with some protesters chanting against the government and the supreme leader, Ayatollah Ali Khamenei.
The protests have put pressure on the clerical leaders in power since the 1979 Islamic Revolution.
President Hassan Rouhani has acknowledged the public's anger over the Islamic Republic's flagging economy, though he and others warned that the government wouldn't hesitate to crack down on those it considers lawbreakers.
All the protest rallies so far haven't received prior permission from the Interior Ministry, making them illegal under Iranian law.
In comments posted to his official website, Mr Khamenei appeared to blame foreign nations for at least exacerbating the unrest gripping Iran.
"In the recent days' incidents, enemies of Iran utilised various means — including money, weapon, politics and intelligence apparatuses — to create problems for the Islamic system," he said.
The head of Tehran's Revolutionary Court also reportedly warned that arrested protesters could potentially face death penalty cases when they come to trial.
Iran's semi-official Tasnim news agency quoted Mousa Ghazanfarabadi as saying: "Obviously one of their charges can be Moharebeh," or waging war against God, a death penalty offence in Iran.
Donald Trump supported the protesters in a tweet: "The great Iranian people have been repressed for many years. They are hungry for food & for freedom. Along with human rights, the wealth of Iran is being looted. TIME FOR CHANGE!"
Later in the day, he tweeted to say "the people of Iran are finally acting against the brutal and corrupt Iranian regime".
"All of the money that President Obama so foolishly gave them went into terrorism and into their 'pockets,"' Mr Trump wrote, apparently referring to the nuclear deal reached under his predecessor. "The people have little food, big inflation and no human rights. The US is watching!"
Iran's Foreign Ministry spokesman, Bahram Ghasemi, urged the US President to stop tweeting and focus on his own country's problems.
"It is better for him to try to address the US' internal issues like the murder of scores killed on a daily basis in the United States during armed clashes and shootings, as well as millions of the homeless and hungry people in the country," Mr Ghasemi said, according to the state-run IRNA news agency.
The protests began over Iran's economy, which has improved since the nuclear deal that saw Iran agree to limit its enrichment of uranium in exchange for the end of some international sanctions. Tehran now sells its oil on the global market and has signed deals to purchase tens of billions of dollars' worth of Western aircraft.
However, the improvement has not reached the average Iranian.
Unemployment remains high, and official inflation has crept up to 10 per cent again. A recent increase in egg and poultry prices by as much as 40 per cent, which the government has blamed on a cull over avian flu fears, appears to have been the spark for the economic protests.
A semi-official news agency reports that 450 people have been arrested over three days of protests in Tehran.
The ILNA news agency report quoted Ali Asghar Nasserbakht, a security deputy governor of Tehran, offering the figure.
Mr Nasserbakht said that 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 has not asked for the help of the Revolutionary Guards special forces.
Mehr news agency also quoted a judiciary official as saying that several ringleaders of protests in Karaj, the fourth largest city in Iran, have been arrested.
The protests began last Thursday over economic issues and expanded to several cities.
No nationwide arrest figures have been released by authorities since the demonstrations began.
Iranian state TV is reporting that nine people have been killed overnight amid nationwide protests and unrest.
The report puts the death toll in six days of demonstrations to at least 20 people.
State TV said six rioters were killed during an attack on a police station in the town of Qahdarijan.
It reported the clashes were sparked by rioters who tried to steal guns from the police station.
State TV also said an 11-year-old boy and a 20-year-old man were killed in the town of Khomeinishahr, while a member of Iran's paramilitary Revolutionary Guard was killed in the town of Najafabad. It said all were shot by hunting rifles.
The towns are all in Iran's central Isfahan province, some 350km (215 miles) south of Tehran.
Arrested protesters could potentially face death penalty cases when they come to trial, the head of Tehran's Revolutionary Court has reportedly warned.
"Obviously one of their charges can be Moharebeh," or waging war against God, the semi-official Tasnim news agency quoted Mousa Ghazanfarabadi as saying.
It is a death penalty offense in Iran.
Mr Ghazanfarabadi was also quoted as saying some protesters will come to trial soon on charges of acting against national security and damaging public properties.
He also stressed that attending rallies not sanctioned by police was illegal in Iran.
Syria has expressed solidarity with Iran and criticised the US and Israel for expressing support to Iranian protesters.
A Syrian Foreign Ministry statement blamed the US and Israel for destabilising the region.
The ministry said Iran's sovereignty should be respected and no one should interfere in Tehran's internal affairs.
"Syria is confident that Iran's leadership, government and people will be able to defeat the conspiracy," the Syrian ministry said.
Syria is Iran's strongest ally in the Arab world and Tehran has been a main backer of Syrian President Bashar al-Assad since the country's conflict began in 2011, pumping hundreds of millions of dollars into the Syrian economy.
Emily Thornberry, the Shadow Foreign Secretary, has called for Iranian authorities to show restraint.
She said: "The picture surrounding the protests in Iran remains highly uncertain, and Western politicians should be cautious in claiming to understand their origins, organisation or objectives, when many Iranian experts are still struggling to do so.
"However, one thing is absolutely clear: the escalation of violence must be stopped, and it is particularly incumbent on the Iranian authorities to show restraint in their policing, allow peaceful, democratic protests to proceed, and enable a political dialogue so that all political and economic grievances can be raised and resolved."
Iran's Supreme Leader has accused enemies of the Islamic Republic of stirring unrest.
"In recent days, enemies of Iran used different tools including cash, weapons, politics and intelligence apparatus to create troubles for the Islamic Republic," Ayatollah Ali Khamenei was quoted as saying in a post on his official website.
Mr Khamenei said he would address the nation about the recent events "when the time is right".
The UK Government thinks there should be meaningful debate in Iran on the issues protesters are raising, Theresa May's spokesman has said.
Britain has called on Iran to engage in meaningful debate about issues raised by protesters, Theresa May's spokesman has said.
"We believe there should be meaningful debate about the legitimate and important issues that the protesters are raising, and we're looking to the Iranian authorities to permit that," the Prime Minister's spokesman said.
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