'We are now willing to...': US threatens secondary sanctions over Iranian oil purchases

Washington has drawn a hard line. The United States on Wednesday threatened to sanction any country still buying Iranian oil, warning China, Tehran's biggest oil customer, to expect disruption as a US maritime blockade takes hold.

"We have told countries that if you are buying Iranian oil, or if Iranian money is sitting in your banks, we are now willing to act," Treasury Secretary Scott Bessent said at the White House.

Bessent was equally direct on China. "We believe (that with) this blockade ... there will be a pause of Chinese buying," he said, adding that US authorities have already contacted two Chinese banks, warning they could face sanctions if Iranian funds are found moving through their systems. Beijing offered no immediate response.

The blockade, launched earlier this week under President Donald Trump, is now in its seventh week of the broader Iran conflict and is designed to cut off Tehran's primary revenue stream. Alongside it, Washington has imposed fresh sanctions on Iran's oil transportation network, targeting individuals, companies and vessels, more than two dozen in total, linked to its shipping operations.

Central to the pressure campaign is China, which has accounted for the bulk of Iran's seaborne oil exports. US officials say the blockade could significantly disrupt that trade.

The administration also confirmed it will not renew a 30-day waiver issued on March 20, which had allowed Iranian oil already at sea to reach buyers. Bessent said the exemption enabled around 140 million barrels to enter global markets. That window closes on April 19.

A similar waiver covering seaborne Russian oil has also been allowed to lapse, further tightening the squeeze on global energy flows.

The moves are part of Washington's longstanding "maximum pressure" campaign against Iran over its nuclear programme and regional activities, a campaign that has struggled to stop Iranian oil from reaching markets, particularly in China. This time, the administration is signalling it intends to enforce with more teeth.

(WIth inputs from Reuters)