The US State Department said on Saturday it had imposed sanctions on a general of Iran's Islamic Revolutionary Guard Corps who commanded units blamed for a massacre of protesters in November.
The US State Department has said previously it had received videos of the Revolutionary Guards opening fire without warning on protesters in Mahshahr county in southwest Iran.
On Saturday, it cited "multiple" media reports and information submitted by the Iranians through its Rewards for Justice tipline that units under Brigadier General Hassan Shahvarpour's command killed as many as 148 people when they used armored vehicles to encircle fleeing protesters, firing machine guns into the crowd and setting fire to the marsh in which protesters took cover.
The State Department said it was designating Shahvarpour, a commander in Khuzestan province where Mahshahr is located, under a US law banning officials of foreign governments and their immediate family members for whom there was "credible information on their involvement in gross violations of human rights."
The announcement comes amid high tensions between Tehran and Washington after the United States killed Iran's most powerful military commander in a drone strike in Iraq and Iran retaliated by launching missile strikes at US targets in Iraq.
US President Donald Trump in 2018 pulled the United States out of a nuclear deal between Iran and major powers, arguing the agreement was too weak and that new sanctions would force Iran to accept more stringent terms.
The State Department, which has stepped up criticism of Iran over human rights, said the latest move demonstrated Washington's "continued commitment to the Iranian people to support their demands for accountability from Iranian officials who committed serious human rights abuses against protesters in November."
A Reuters special report last month found that about 1,500 people were killed during less than two weeks of unrest that started in Iran on Nov. 15. The figures, provided by three Iranian interior ministry officials, included at least 17 teenagers and about 400 women as well as some members of the security forces and police.
Iran's authorities have disputed the US account of what happened at Mahshahr. Iranian officials have said security forces confronted "rioters" who they described as a security threat to petrochemical complexes and to a key energy route that, if blocked, would have created a crisis in the country.