The new measures come amid a standstill in diplomacy after Trump halted US-Israeli attacks against Iran, and were announced just two weeks before Trump visits China, a key customer for Iran's oil.

The United States since President Donald Trump's first term has unilaterally sought to stop all other countries from buying oil from Iran, whose ruling clerics are sworn foes of Israel and the United States.

The State Department said the United States was imposing sanctions on Qingdao Haiye Oil Terminal Co., Ltd., which it said has imported "tens of millions of barrels" of Iranian crude oil, helping Iran generate billions of dollars.

"So long as Iran attempts to generate oil revenues to fund its destabilizing activities, the United States will hold both Iran and all its sanctions-evading partners accountable," the State Department said.

The sanctions will criminalize any transactions involving the United States through the terminal operator, part of the major maritime hub of Qingdao on the Yellow Sea.

The United States last year imposed similar sanctions on another entity in the area, Qingdao Port Haiye Dongjiakou Oil Products Co.

Global oil prices have soared since the US-Israeli attack after Iran in retaliation virtually blocked the Strait of Hormuz, a key waterway for energy transit.

Iran has demanded that the United States end sanctions and a naval blockade. It has vowed to impose "tolls" for ships going through the Strait of Hormuz, despite loud protests from Trump.

The Treasury Department's Office of Foreign Assets Control issued an alert to warn people from and outside the United States about sanctions risks of making payments to Iran's government for safe passage through the Strait of Hormuz.

It also said it was imposing sanctions on three Iranian foreign currency exchange houses, saying they converted oil revenue into more usable currencies.

US Treasury Secretary Scott Bessent said that his agency would "relentlessly target the regime's ability to generate, move and repatriate funds, and pursue anyone enabling Tehran's attempts to evade sanctions."