President Donald Trump has said the US will take "very strong action" against Iran if it executes protesters, as rights groups say more than 2,400 anti-government demonstrators have been killed in a violent crackdown by Iranian authorities.

Relatives of 26-year-old Erfan Soltani, who was detained last week, told BBC Persian he was due to be executed on Wednesday. It is unclear whether this has taken place. 

A representative from the Hengaw Organization for Human Rights also told the BBC that they had "never witnessed a case move so quickly".

Speaking to the BBC's US partner CBS News, Trump said of potential executions: "If they hang them, you're going to see some things... We will take very strong action if they do such a thing."

Soltani's relative told BBC Persian that an Iranian court had issued a death sentence "in an extremely rapid process, within just two days". 

They were "deeply concerned that he could be executed without any prior notice", given that contact with Iran has been affected by the internet shutdown. 

Soltani's detention demonstrated that the Iranian government was trying "to control the population, to not allow any more protests to happen", Hengaw representative Awyar Shekhi told the BBC's Radio 4 Today programme on Wednesday.

Soltani's sister - who is a lawyer - tried to intervene in his case but was told by authorities there was nothing to pursue, Shekhi added.

Prisoners sentenced to death in Iran are typically granted final moments with loved ones. While the Iranian authorities have told the family they will allow a meeting with Erfan before his execution, Shekhi said, he hasn't been allowed any contact with his family since his arrest.

| Hengaw Organization for Human Rights/X (Pic): Erfan Soltani, 26, was detained on Thursday last week

An Iranian official told Reuters that 2,000 people had been killed, but that "terrorists" were to blame. 

Trump earlier said he planned to attend a meeting at the White House on Tuesday night to discuss the situation in Iran, pledging to get "accurate numbers" on the death toll from the protests.

"The killing looks like it's significant, but we don't know yet for certain," Trump told reporters while returning to the White House. 

Once he has the numbers, he said, "we'll act accordingly."

The US-based Human Rights Activists News Agency (HRANA) said that it had so far confirmed the killing of 2,403 protesters, as well as 12 children, despite an internet blackout. Nearly 150 people affiliated with the government have also been killed, the group said.

State-linked Iranian news agency Fars reported that funerals were held in Tehran on Wednesday for more than 100 members of the security forces and others they described as "martyrs".

On Tuesday, Trump wrote on his Truth Social platform that Iranian authorities would "pay a big price" for the killings, and urged people to "keep protesting".

"I have cancelled all meetings with Iranian Officials until the senseless killing of protesters STOPS. HELP IS ON ITS WAY. MIGA!!!," he added, using the acronym for a US-based Iranian opposition slogan, "Make Iran Great Again".

Trump has been weighing military and other options in response to the crackdown, having already announced 25% tariffs on any country trading with Iran.

Iran's government has responded by accusing the US of seeking to "manufacture a pretext for military intervention", warning that "this playbook has failed before".

The protests, which have reportedly spread to 180 cities and towns in all 31 provinces, were sparked by anger over the collapse of the Iranian currency and soaring cost of living.

They quickly widened into demands for political change and became one of the most serious challenges to the clerical establishment since the 1979 Islamic revolution.

Demonstrations escalated significantly last Thursday and were met with deadly force by authorities, masked by a near total shutdown of the internet and communication services.

More than 18,434 protesters have been arrested during the unrest, according to HRANA.

It is difficult to gauge the true scale of bloodshed because, like other international news organisations, the BBC is not able to report from inside the country.

However, videos posted online on Sunday showed people searching for the bodies of their loved ones at the Kahrizak Forensic Centre in Tehran. The BBC counted at least 180 shrouded bodies and body bags in the footage. 

Around 50 bodies were visible in another video from the facility shared on Monday.

"My friend went there [Kahrizak] to look for his brother, and he forgot his own sorrow," an activist told BBC Persian on Monday.

"They piled up bodies from every neighbourhood, like Saadatabad, Naziabad, Sattarkhan. So you go to your address pile and search there. You don't know a fraction of the level of violence that's been used."

Hospitals in the capital have also reportedly been overwhelmed by the number of casualties.

Prof Shahram Kordasti, an Iranian oncologist based in London, told the BBC's Newsday programme on Tuesday that the last message he had received from a colleague in Tehran said: "In most hospitals, it's like a warzone. We are short of supplies, short of blood."

Other doctors at "two to three hospitals" had also said they had treated hundreds of injured or dead people, he added.

An Iranian living in Rasht, near the Caspian Sea coast, described the city as unrecognisable. "Everywhere is burnt with fire," they said.

The UN human rights chief Volker Türk urged Iranian authorities to halt all forms of violence and repression against peaceful protesters immediately, his office said.

He added that the labelling of protesters as "terrorists" to justify violence was unacceptable and that it was "extremely worrying" to see statements from Iranian officials indicating the possibility of the death penalty being used against protesters through expedited trials.

Iran's Judiciary chief Gholamhossein Mohseni Ejei said on Monday that those involved in the unrest would be "dealt with seriously and severely". And prosecutors have said some will be charged with "enmity against God", a national security offence that carries the death penalty.

Türk also demanded that Iranian authorities restore full access to the internet and other communication services.

Some international calls from Iran went through on Tuesday, but the internet shutdown has now passed 132 hours, according to monitor NetBlocks.

One person living near Tehran with access via the Starlink satellite service told BBC Persian that there were "checkpoints in every block", where cars and the phones of their occupants were being inspected by security forces.

New videos of protests in recent days have also emerged, with BBC Persian verifying those filmed in the central city of Arak and the western cities of Tabriz, Urmia and Khorramabad.

In the footage from Khorramabad, gunfire can be heard during clashes between security forces and protesters, some of whom are throwing stones.

The protesters chant slogans "Death to the dictator" - a reference to Ayatollah Khamenei - and "Reza Shah, may your soul rest in peace" - referring to the late monarch Mohammad Reza Pahlavi, who was overthrown in the 1979 revolution and whose son Reza lives in exile.