The United States on Thursday imposed sanctions on the Iranian judge who sentenced a recently freed American and vowed more punishment over the suppression of protests.

US officials said that Abdolghassem Salavati, a Revolutionary Court judge in Tehran, has sentenced more than 100 people to jail or death for political reasons and pointed to his role in the imprisonment of Xiyue Wang.

The Princeton scholar researching Iranian history was arrested in 2016 on espionage charges but freed earlier this month in a swap for an Iranian jailed in the United States.

"We're glad we won Xiyue's release but he should never have been sentenced or jailed in the first place," Secretary of State Mike Pompeo told a forum on human rights dominated by Iranian exiles.

"He's a tool of the regime's suppression, not an impartial friend of justice," he said of Salavati.

The Treasury Department also targeted another Revolutionary Court judge, Mohammad Moghisseh, who it said has presided over trials of artists and over anti-regime social media postings.

The sanctions make any transactions with the two judges a crime in the United States, with any assets they may have blocked.

Pompeo said that the United States would also restrict visas for Iranian officials over last month's crackdown on protests, in which Amnesty International says more than 300 people died.

US Secretary of State Mike Pompeo waves after delivering remarks on human rights in Iran at the State Department
US Secretary of State Mike Pompeo waves after delivering remarks on human rights in Iran at the State Department AFP / Olivier Douliery

The restrictions will also apply to the officials' families, Pompeo said.

"Thugs killing people's children will not be allowed to send their own children to study in the United States of America," Pompeo said.

President Donald Trump's administration has already ended the vast majority of new visas for Iranians as part of a crackdown on immigration from mostly Muslim countries.

Trump has imposed sweeping unilateral sanctions on Iran, trying to stop all its oil sales, and boasted of the damage to the Iranian economy.

Pompeo said, however, that the United States was acting "for the sake of human dignity" in Iran.

"America hears you, America supports you, America stands with you," he said.