WASHINGTON (BLOOMBERG) - The US has filed court documents in a bid to seize oil on board a vessel because it says the crude came from Iran and falls under its terrorism laws.

The Department of Justice issued a complaint in a US district court to seize the cargo on the Liberia-flagged Achilleas on Tuesday (Feb 2), according to a statement.

The US alleges that Iran's Islamic Revolutionary Guard Corps and the IRGC-Qods Force covertly shipped Iranian oil to a customer abroad.

"Participants in the scheme attempted to disguise the origin of the oil using ship-to-ship transfers, falsified documents, and other means, and provided a fraudulent bill of lading to deceive the owners of the Achilleas into loading the oil in question," the department said.

The Achilleas' Greek owner, Capital Ship Management Corp, alerted US authorities to the possibility that it had unknowingly taken on Iranian crude, after initially thinking it came from Iraq, Bloomberg reported last month.

Washington ordered the ship to sail to the US before Mr Joe Biden succeeded Mr Donald Trump as US President on Jan 20, according to people familiar with the matter.

Under Mr Trump, Washington tightened sanctions on Iran in an effort to halt its oil sales, end its nuclear activities and stop what the US considers to be its interference in other Middle Eastern countries.

"The US Attorney's Office for the District of Columbia will continue working with our law enforcement partners to stem the flow of illicit oil from Iran's Islamic Revolutionary Guard Corps and Qods Force," Acting US Attorney Michael Sherwin said in the statement.

The vessel is fully loaded with more than two million barrels, according to shipping documents.

It's heading to the US and is currently sailing close to the South American coast, according to tracking data compiled by Bloomberg.

The US will need to prove its allegations in court proceedings, said the statement.