China told its independent refineries to disregard U.S. sanctions over their purchases of Iranian crude.
The measures aim to crack down on Iran’s shadow banking system and Chinese purchases of Iranian oil.
President Trump withdrew from the Obama-era nuclear accord in 2018, saying it was the worst deal ever. But Iran responded with an enrichment spree that haunts the negotiations to this day.
The Treasury Department also targeted a top independent Chinese refinery that it said was a major buyer of Iranian petroleum.
The conflict has morphed into a volatile standoff in the Strait of Hormuz, as the economic costs mount and President Trump faces a political backlash at home.
President Trump has ridiculed President Barack Obama and the agreement, which he withdrew from during his first term. His critics say he could have avoided a war had he left it in place.
With the cease-fire on the verge of ending, President Trump said on Tuesday that he would keep it in place until Iran’s “proposal is submitted, and discussions are concluded, one way or the other.”
Iranian leaders fear being burned again by President Trump, who tore up a nuclear agreement reached during the Obama administration after lengthy negotiations.
As the United States and Iran make a second attempt at a deal, their negotiating styles are on a collision course.
The vice president is again center stage, after abruptly leaving the first round of high-level Iranian peace talks without an agreement.