Iran's supreme leader has for the first time publicly acknowledged that thousands of people were killed during recent protests.
In a speech on Saturday, Ayatollah Ali Khamenei said thousands had been killed, "some in an inhuman, savage manner", and blamed the US for the deaths.
A violent response to the unrest has claimed 3,090 lives, according to US-based Iranian Human Rights Activists News Agency (HRANA), with some activist groups putting the death toll far higher. An internet blackout has made it extremely difficult to get clear information.
US President Donald Trump recently urged Iranian demonstrators to "keep protesting" and threatened military intervention if security forces kill them.
"Those linked to Israel and the US caused massive damage and killed several thousand," Khamenei said, quoted by Iranian state media.
"We consider the US president criminal for the casualties, damages and slander he inflicted on the Iranian nation."
The protests, which began on 28 December over the economy, have turned into calls for the end of the rule of Iran's supreme leader.
The Iranian government has called the demonstrations "riots" backed by Iran's enemies.
Protesters have been met with deadly force and videos of security forces shooting at demonstrations have been authenticated by both BBC Persian and BBC Verify.
There has also been a near-total shutdown of the internet and communication services in Iran. On Saturday overall connectivity remained at about 2% of ordinary levels, according to cyber monitor NetBlocks.
There have been fewer reports of unrest in recent days but with internet access still restricted developments on the ground remain unclear.
A woman in Shiraz, south-western Iran, told BBC Persian that "security forces are still patrolling on motorbikes to keep the situation under control, but overall things have gone back to normal".
During his speech on Saturday, Khamenei also said Iran considered President Trump to be a "criminal" and said the US must be "held accountable" for recent unrest.
He also claimed on social media that "America's goal is to swallow Iran".
Trump has not yet responded to the supreme leader and the BBC has approached the White House for a comment.
The US state department said on Saturday that it had "heard reports that the Islamic Republic is preparing options to target American bases".
It said Iran would be met with "a very, very powerful force" if it launched such an attack and warned Tehran not to "play games with President Trump".
The US president said on Wednesday he had been told "the killing in Iran has stopped", but added that he had not ruled out military action against the country.
His comments came after the US and UK both reduced the number of personnel at the Al-Udeid air base in Qatar.
Officials told CBS, the BBC's US partner, that a partial American withdrawal was a "precautionary measure".