Iranian authorities indicated on Saturday that they could intensify their crackdown on the largest anti-government demonstrations in years, with the Revolutionary Guards blaming unrest on "terrorists" and vowing to safeguard the governing system.

According to details, US President Donald Trump, who has repeatedly threatened to intervene in recent days, posted on social media on Saturday: "Iran is looking at FREEDOM, perhaps like never before. The USA stands ready to help!!!"

Fresh reports of violence emerged across Iran, although an internet blackout made it difficult to assess the full extent of the unrest. After nightfall on Saturday, new videos posted online purportedly showed protests in several neighbourhoods of the capital, Tehran, and in other cities, including Rasht in the north, Tabriz in the north-west, and Shiraz and Kerman in the south. Reuters could not immediately verify the latest videos.

The exiled son of Iran's last shah, who has become a prominent voice within the fragmented opposition, issued his strongest call yet for the protests to broaden into a revolt aimed at toppling the clerical rulers.

State media reported that a municipal building was set on fire in Karaj, west of Tehran, and blamed "rioters". State television broadcast footage of funerals for members of the security forces said to have been killed in protests in Shiraz, Qom and Hamedan.

Footage posted on Friday on social media showed large crowds gathered in Tehran and fires set in the streets. In one video, verified by Reuters, showing a nighttime protest in Tehran’s Saadatabad district, a man is heard saying that the crowd had taken control of the area.

"The crowd is coming. 'Death to the dictator', 'Death to Khamenei'," he said, referring to Supreme Leader Ayatollah Ali Khamenei.

Protests have spread across Iran since December 28, initially in response to soaring inflation, before quickly turning political, with demonstrators demanding an end to clerical rule. Authorities have accused the US and Israel of fomenting unrest.

A senior US intelligence official described the situation as an "endurance game". The opposition is attempting to maintain pressure until key government figures either flee or switch sides, while the authorities aim to sow enough fear to clear the streets without giving the United States justification to intervene, the official said.

Iranian rights group HRANA reported that at least 50 protesters and 15 security personnel have been killed, and some 2,300 people arrested.

Army Says 'Terrorist Groups' Seek to Undermine Security

A witness in western Iran, reached by phone, said the Revolutionary Guards (IRGC) were deployed and firing in the area from which the witness was speaking, declining to be named for safety reasons.

The semi-official Tasnim news agency reported the arrest of 100 "armed rioters" in the town of Baharestan, near Tehran.

In a statement broadcast by state television, the IRGC – an elite force that 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 alight.

Safeguarding the achievements of the Islamic revolution and maintaining security was described as a "red line".

The regular military also issued a statement saying it would "protect and safeguard national interests, the country’s strategic infrastructure and public property".

Pahlavi Says Goal Is to Prepare to 'Seize City Centres'

In a video posted on X, US-based Reza Pahlavi, 65, whose father was toppled as Iran’s shah in the 1979 revolution, said the Islamic Republic would be brought "to its knees". He urged people to seize the centres of their towns and said he was preparing to return soon to Iran.

"Our goal is no longer merely to come into the streets; the goal is to prepare to seize city centres and hold them," he said.

A doctor in north-western Iran said that since Friday, large numbers of injured protesters had been brought to hospitals. Some were badly beaten, with head injuries, broken arms and legs, and deep cuts.

At least 20 people in one hospital had been shot with live ammunition, five of whom later died.

Trump said on Thursday that he was not inclined to meet Pahlavi, signalling that he was waiting to see how the crisis develops before backing an opposition leader.

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 following the death in custody of a woman accused of violating dress codes.

Trump, who joined Israel in strikes on Iran’s nuclear sites last summer, has included Iran in lists of countries in which he could intervene, since sending forces to seize the president of Venezuela a week ago. On Friday, in a warning to Iran’s leaders, he said: "You better not start shooting because we'll start shooting too."

Some protesters on the streets have shouted slogans in support of Pahlavi, such as "Long live the shah", although most chants have called for an end to clerical rule or demanded action to address the economic crisis.

On Friday, Khamenei accused protesters of acting on behalf of Trump, saying rioters were attacking public property and warning that Tehran would not tolerate people acting as "mercenaries for foreigners".