- Video report by ITV News International Affairs Editor Rageh Omaar
Nine people, including a number of rioters who tried to storm a police station, have been killed in clashes overnight between anti-government protesters and police in Iran, according to state television.
The reports on Tuesday bring the death toll to at least 20 as the protests continue into a sixth day.
In his first remarks since the protests began, Iran's supreme leader, Ayatollah Ali Khamenei, accused "enemies of Iran" of using "various means" to meddle in the country.
But the US continued to foment the protests, calling on the regime to end its new block on social media sites.
Donald Trump tweeted on Tuesday that it was "time for change," while the State Department said the US had "obligation not to stand by".
The US called on Iran to "open these sites" including Instagram and the messaging app Telegram.
Boris Johnson, the British foreign secretary, earlier said the UK was "watching events in Iran closely".
The demonstrations - the largest to hit Iran since the protests around the disputed 2009 election - began in Mashhad, apparently over rising food prices, and expanded to several cities.
Hundreds of people have been arrested, including 450 people arrested in Tehran over three days, according to a report by the semi-official ILNA news agency.
Following the clashes overnight, state TV reported that six rioters had been killed during an attack on a police station in the town of Qahdarijan when they tried to steal guns from the facility.
In the town of Khomeinishahr, an 11-year-old boy and a 20-year-old man were killed, state TV said.
A member of Iran's paramilitary Revolutionary Guard was also reported killed in the town of Najafabad.
It was unclear if this was the same fatality as that reported by Iran's semi-official Mehr news agency on Monday.
Mehr reported a gunman had killed a policeman and wounded three other officers during a protest in the same location - the first reported fatality among Iran's security forces.
Iran's President Hassan Rouhani has acknowledged the public's anger over the flagging economy, but he has also warned that rioters and looters will be arrested.
That was echoed Monday by judiciary chief Ayatollah Sadegh Larijani, who urged authorities to confront rioters, state TV reported.
"I demand all prosecutors across the country to get involved and the approach should be strong," he said.
On Tuesday, the head of Tehran's Revolutionary Court reportedly warned that arrested protesters might potentially face the death penalty.
Iran's semi-official Tasnim news agency quoted Mousa Ghazanfarabadi as saying: "Obviously one of their charges can be Moharebeh," which is waging war against God, a death penalty offense in Iran.
Syria, an Iranian ally in the region, expressed solidarity with Iran, with a foreign ministry statement blasting the US and Israel for expressing their support for the protests.