The recent seizure of an oil tanker known as Skipper by the U.S. off the coast of Venezuela marks a dramatic escalation of President Donald Trump’s campaign to choke off Venezuelan leader Nicolás Maduro’s access to oil revenues.

The U.S. Coast Guard, with the help of the FBI and Homeland Security Investigations, executed a seizure warrant Wednesday for a crude oil tanker that was allegedly used to transport oil from Venezuela and Iran in defiance of sanctions, Attorney General Pam Bondi said. A White House official confirmed it was carrying oil from PDVSA.

Venezuela’s foreign affairs minister denounced the seizure, calling it a “blatant theft” and “an act of international piracy.”

President Trump was not clear on what the U.S. plans to do with the oil from a Venezuelan tanker that was seized on Wednesday. Meanwhile, questions are emerging about the fate of the crew aboard the oil ship.