Donald Trump again promises America 'stands ready to help' Iran's protesters in major challenge to Ayatollah

Meanwhile, the Revolutionary Guards are blaming unrest on terrorists and are vowing to safeguard the governing system.

Now President Trump, who has repeatedly threatened to intervene in recent days, has suggested the US could step in to support.

Writing on his Truth Social page, President Trump said: "Iran is looking at FREEDOM, perhaps like never before. The USA stands ready to help!!!"

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, with a senior US intelligence official described the situation as an "endurance game".

The opposition was trying to keep up pressure until key government figures either flee or switch sides, while the authorities were trying to sow enough fear to clear the streets without giving the United States justification to intervene, the official said.

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

After nightfall on Saturday, new videos posted online purported to show fresh protests in a number of neighbourhoods in the capital Tehran and several cities, including Rasht in the north, Tabriz in the northwest and Shiraz and Kerman in the south.

The exiled son of Iran's last Shah, 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.

In one video showing a nighttime protest in north Tehran's Sa'adat Abad district, a man is heard saying the crowd had taken over the area, shouting: "The crowd is coming. Death to the dictator, 'Death to Khamenei" referring to Supreme Leader Ayatollah Ali Khamenei.

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 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 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.

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 called for people to seize the centres of their towns, and said he was preparing to return soon to Iran.

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

President Trump said on Thursday he was not inclined to meet Pahlavi, a sign that he was waiting to see how the crisis plays out before backing an opposition leader.

President Trump, who joined Israel to strike Iran's nuclear sites last summer, has included Iran in lists of places 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 rule by the clerics or demanded action to fix the economy.

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