Speaking at the White House, Trump said he had received assurances from “very important sources on the other side” that the killings had stopped and that planned executions would not go ahead.
He offered no details and noted that the United States had yet to verify the claims.
“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.
“We’ve been told on good authority, and I hope it’s true.”
Iran struck a defiant tone, however, warning it could respond to any attack, as Washington appeared to draw down staff at a base Tehran targeted in a strike last year.
The standoff between the two foes, who have had no diplomatic ties since the 1979 Islamic revolution, follows Trump’s warning that Tehran could face action over a crackdown on protests that rights groups say has left at least 3,428 people dead.
Rights monitors say that under cover of a five-day internet blackout, Iranian authorities are carrying out their harshest repression in years against demonstrations openly challenging the theocratic system.
Foreign minister Abbas Araghchi told US network Fox News the government was “in full control” and reported an atmosphere of “calm” after what he called three days of “terrorist operation.”
Iran’s judiciary chief vowed fast-track trials for those arrested, stoking fears authorities will use capital punishment as a tool of repression.
In Tehran, authorities held a funeral for more than 100 security personnel and other “martyrs” killed in the unrest, which officials have branded “acts of terror.”
Two diplomatic sources told AFP some personnel have been asked to leave the Al Udeid US military base in Qatar, with the Gulf state citing “regional tensions” as the reason.
Iran targeted the base in June in retaliation for US strikes on its nuclear facilities. Ali Shamkhani, a senior advisor to supreme leader Ayatollah Ali Khamenei, warned Trump the strike showed “Iran’s will and capability to respond to any attack.”
The British government said meanwhile that its embassy in Tehran had been “temporarily closed,” while the US embassy in Saudi Arabia urged staff to exercise caution and avoid military installations.
Trump told CBS News on Tuesday the United States would “take very strong action” if Iran began hanging protesters.
G7 nations said Wednesday they were “deeply alarmed at the high level of reported deaths and injuries” and warned of further sanctions if the crackdown continued.
Judiciary chief Gholamhossein Mohseni Ejei, visiting a prison holding protest detainees, said on state TV that “if a person burned someone, beheaded someone and set them on fire then we must do our work quickly.”
He called for public trials, according to Iranian news agencies, and said he had spent five hours reviewing cases in Tehran.
Monitor NetBlocks said Iran’s internet blackout had lasted 144 hours. Despite the shutdown, new videos, with locations verified by AFP, showed bodies lined up in the Kahrizak morgue south of Tehran, wrapped in black bags as distraught relatives searched for loved ones.
Amnesty International accused authorities of committing mass unlawful killings “on an unprecedented scale,” citing verified videos and eyewitness accounts.