The U.S. is renewing pressure on Iran, aiming to drive exports of Iranian oil down to zero.

Sources told Reuters the U.S. is expected to announce that all countries must end imports of Iranian oil, or face sanctions themselves.

The sources confirmed a report by a Washington Post columnist saying that the U.S. would end sanctions waivers granted to some importers of Iranian oil late last year.

That's after U.S. President Donald Trump pulled the U.S. out of the 2015 Iran nuclear deal, and then reimposed sanctions on exports of Iranian oil in late November.

At the time, Washington granted waivers to eight economies that had reduced their purchases of Iranian oil.

The waivers would allow them to continue to import from Iran without incurring sanctions for six more months.

The Washington Post columnist also reported that the State Department will no longer be granting these waivers as of May 2nd, citing two unnamed officials.

The news triggered a spike in oil prices, driving the benchmark Brent crude oil futures up more than 3 percent on Monday (April 22).

Asian economies are likely to be hit hard.

Iran's biggest oil customers are China and India, who have both lobbied for extensions to the sanctions waivers.

South Korea is also a big buyer - its refining industry relying on an ultra-light form of crude oil to produce petrochemicals.

Washington is pressuring Iran to stop its nuclear program, as well as to stop backing militant proxies in the Middle East.

They've adopted a campaign of maximum economic pressure, imposing sanctions on oil exports to reduce Tehran's main source of revenue.