Washington DC - President Donald Trump threatened Iran with "very strong action" if it goes ahead with the hanging of people involved in nationwide protests that have rocked the country.

International outrage has built over the crackdown on a protest movement posing one of the biggest challenges yet to Iran's clerical leadership.

Iran's UN mission posted a statement on X, vowing that Washington's "playbook" would "fail again."

"US fantasies and policy toward Iran are rooted in regime change, with sanctions, threats, engineered unrest, and chaos serving as the modus operandi to manufacture a pretext for military intervention," the post said.

Politicians Gavin Newsom slams Karoline Leavitt over claims that Democrats are "protecting" pedophiles

Iranian authorities have insisted they had regained control of the country after successive nights of mass demonstrations nationwide.

Rights groups accuse the government of fatally shooting hundreds of protesters and masking the scale of the crackdown with an internet blackout that has now surpassed the five-day mark.

New videos on social media, with locations verified by AFP, showed bodies lined up in the Kahrizak morgue just south of the Iranian capital, with the corpses wrapped in black bags and distraught relatives searching for loved ones.

The State Department on its Farsi language X account said 26-year-old protestor Erfan Soltani had been sentenced to be executed on Wednesday.

"Erfan is the first protester to be sentenced to death, but he won't be the last," the State Department said, adding more than 10,600 Iranians had been arrested.

Amnesty International also called on Iran to immediately halt all executions, including Soltani's.

Donald Trump Trump claims white people have been treated "very badly" because of civil rights

Iranian state media has said dozens of members of the security forces have been killed, with their funerals turning into large pro-government rallies.

Trump – who earlier told the protesters in Iran that "help is on its way" – said Tuesday in a CBS News interview that the US would act if Iran began hanging protesters.

Tehran prosecutors have said Iranian authorities would press capital charges of "moharebeh," or "waging war against God," against some suspects arrested over recent demonstrations.

"We will take very strong action if they do such a thing," said Trump, who has repeatedly threatened Iran with military intervention, having already bombed the country last year.

"When they start killing thousands of people – and now you're telling me about hanging. We'll see how that's going to work out for them," he added.