US President Donald Trump has warned of unspecified "very strong action" if Iranian authorities go ahead with threatened hangings of some protesters, with Tehran calling American warnings a "pretext for military intervention".
Trump — who earlier told the protesters in Iran that "help is on its way" — said on Tuesday in a CBS News interview that the United States 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 the US president, who has repeatedly threatened Iran with military intervention.
"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," Trump said.
The US State Department on its Farsi language X account said 26-year-old protester 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.
Iran's UN mission, meanwhile, 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.
Iranian state media has said dozens of members of the country's security forces have been killed, with their funerals turning into large pro-government rallies.
Authorities in Tehran have announced a mass funeral ceremony in the capital on Wednesday for the "martyrs" of recent days.
Rights groups accuse the government of fatally shooting protesters and masking the scale of the crackdown with an internet blackout that has now surpassed the five-day mark.
Iranian authorities have insisted they had regained control of the country after successive nights of mass protests nationwide since.
