Washington DC - The US unveiled sanctions Friday targeting Iran's "shadow fleet" said to be supporting the country's oil exports, as Washington steps up pressure over the government's crackdown on protesters.

The Treasury Department took aim at nine vessels and their respective owners or management firms, which US officials said "collectively transported hundreds of millions of dollars' worth of Iranian oil and petroleum products to foreign markets."

The department charged that revenue from these products is being diverted to fund "regional terrorist proxies, weapons programs, and security services."

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The move comes as a US-based rights group said that it had confirmed the deaths of more than 5,000 people during protests that swept Iran, adding that most of them were demonstrators targeted by security forces.

A fortnight of protests starting in late December shook Iran's clerical leadership under Supreme Leader Ayatollah Ali Khamenei. But the movement has petered out in the face of a crackdown that activists say killed thousands, accompanied by an unprecedented internet blackout.

NGOs tracking the effects of the crackdown have said their work has been hampered by a now two-week internet shutdown, warning that confirmed figures are likely to be far below the actual toll.

The US Treasury's targets unveiled Friday included firms based in the United Arab Emirates, India, and Oman.

"Today's sanctions target a critical component of how Iran generates the funds used to repress its own people," US Treasury Secretary Scott Bessent said in a statement.

"Treasury will continue to track the tens of millions of dollars that the regime has stolen and is desperately attempting to wire to banks outside of Iran," he added.

In a separate statement, the US State Department added that "this latest action will further restrict Iran's ability to export petroleum and petroleum products through obscure and fraudulent mechanisms."

This is also aimed at further constraining "its ability to bankroll the repression of Iranians and international malign behavior," State Department spokesman Tommy Pigott said.