Washington DC - President Donald Trump said Wednesday he had been told the killings of protesters in Iran had been halted, but added that he would "watch it and see" about threatened military action.

Trump had repeatedly talked in recent days about coming to the aid of the Iranian people over the crackdown on protests that rights groups say has left at least 3,428 people dead.

But in a surprise announcement at the White House, Trump said he had now received assurances from "very important sources on the other side" that Tehran had now stopped, and that executions would not go ahead.

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"They've said the killing has stopped and the executions won't take place – there were supposed to be a lot of executions today, and that the executions won't take place – and we're going to find out," Trump said.

He offered no details and noted that the US had yet to verify the claims.

Asked by an AFP reporter in the Oval Office if US military action was now off the table, Trump replied: "We're going to watch it and see what the process is."

Iranian Foreign Minister Abbas Araghchi later said there would be "no hanging today or tomorrow," in an interview with US network Fox News.

"I can tell you, I'm confident that there is no plan for hanging," Araghchi said, also accusing Israel of orchestrating violence, without providing evidence.

A rights group said separately that the execution of an Iranian man arrested during the wave of protests, 26-year-old Erfan Soltani, would not take place as scheduled on Wednesday, citing relatives.

But Araghchi said the Iranian government was "in full control" and reported an atmosphere of "calm" after what he called three days of "terrorist operation."