The U.S. is trying to seize around 2 million barrels of what it thinks is Iranian oil, according to people familiar with the matter, in Washington’s latest attempt to block the Islamic Republic’s energy exports. The crude is on board the Liberia-flagged Achilleas, which is sailing to the U.S. after the Department of Justice issued a seizure order, said the people, who asked not to be identified as they’re not authorized to speak to media.

The order came before Joe Biden succeeded Donald Trump as U.S. president on Jan. 20, according to the people. Under Trump, Washington tightened sanctions on Iran in an effort to halt its oil sales, end its nuclear activities and stop it interfering in other Middle Eastern countries.

The Achilleas’ Greek owner, Capital Ship Management Corp., alerted U.S. authorities to the possibility it had unknowingly taken on Iranian crude, after initially believing it came from Iraq, said the people. The vessel is fully loaded and can carry more than 2 million barrels, according to shipping documents.