The US-based Human Rights Activists News Agency gave the new figure, saying arrests had reached more than 2600 people. The agency has been accurate in multiple rounds of unrest previously.
Supreme Leader Ayatollah Ali Khamenei has signalled a coming clampdown, despite US warnings from President Donald Trump that America could intervene to protect peaceful demonstrators.
Tehran escalated its threats Saturday, local time, with Iran's attorney general, Mohammad Movahedi Azad, warning that anyone taking part in protests will be considered an "enemy of God", a death-penalty charge.
A day after US President Donald Trump issued a new warning that the United States could intervene, there were fresh reports of violence across the country, although an internet blackout made it difficult to assess the full extent of unrest.
The exiled son of Iran's last shah, Reza Pahlavi, who has emerged as a prominent voice in the fragmented opposition, made his strongest call yet for the protests to broaden into a revolt to topple the clerical rulers.
State media said a municipal building was set on fire in Karaj, west of Tehran, and blamed "rioters".
State TV broadcast footage of funerals of members of the security forces it said were killed in protests in the cities of Shiraz, Qom and Hamedan.
Footage posted on social media showed large crowds gathered in Tehran and fires lit in the street at night.
In a video showing a night-time protest in Tehran's Saadatabad district, a man is heard saying the crowd had taken over the area.
"The crowd is coming. 'Death to the dictator', 'Death to Khamenei'," he said, referring to Supreme Leader Ayatollah Ali Khamenei.
Reuters verified the locations of the videos.
Protests have spread across Iran since December 28, beginning in response to soaring inflation and quickly turning political with protesters demanding an end to clerical rule.
Authorities accuse the US and Israel of fomenting unrest.
A witness in western Iran reached by phone said the Revolutionary Guards (IRGC) were deployed and opening fire in the area from which the witness was speaking, declining to be identified for safety.
The Tasnim news agency reported the arrest of 100 "armed rioters" in the town of Baharestan near Tehran.
The IRGC's intelligence wing said it had arrested a foreigner suspected of spying for Israel, the news agency reported on Saturday.
In a statement broadcast by state TV, the IRGC - an elite force which has suppressed previous bouts of unrest - accused "terrorists" of targeting military and law enforcement bases over the past two nights.
It said several citizens and security personnel had been killed and public and private property set on fire.
Safeguarding the achievements of the Islamic revolution and maintaining security was a "red line", it added.
The regular military also issued a statement saying it would "protect and safeguard national interests, the country's strategic infrastructure, and public property".
Iran's rulers have weathered repeated bouts of unrest, including student protests in 1999, over a disputed election in 2009, against economic hardships in 2019 and in 2022 over the death in custody of a woman accused of violating dress codes.
A doctor in northwestern Iran said that since Friday large numbers of injured protesters had been brought to hospitals.
Some were badly beaten, suffering head injuries and broken legs and arms, as well as deep cuts.
At least 20 people in one hospital had been shot with live ammunition, five of whom later died.
The IRGC's public relations office said three members of the Basij security force were killed and five wounded during clashes with what it described as "armed rioters" in Gachsaran, in the southwest.
With AP
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