Iranian security forces may have killed more than 1,000 people since protests over gasoline price hikes began in mid-November, U.S. Special Representative for Iran Brian Hook said on Thursday.
"As the truth is trickling out of Iran, it appears the regime could have murdered over a thousand Iranian citizens since the protests began," Hook told reporters at a briefing at the State Department.
He added that "many thousands of Iranians" had also been wounded and at least 7,000 detained in Iran's prisons.
The unrest, which began on Nov. 15 after the government abruptly raised fuel prices by as much as 300%, spread to more than 100 cities and towns and turned political as young and working-class protesters demanded clerical leaders step down.
Tehran has given no official death toll but Amnesty International said on Monday it had documented the deaths of at least 208 protesters, making the disturbances the bloodiest since the 1979 Islamic Revolution.
Tehran's clerical rulers have blamed "thugs" linked to its opponents in exile and the country's main foreign foes - the United States, Israel and Saudi Arabia - for the unrest.