The U.S. has seized a North Korean cargo ship that it alleges has been used to illicitly export coal from the country in violation of international sanctions, the Department of Justice announced Thursday. The move, though many months in the making, is sure to stir resentment in Pyongyang as the two countries try to negotiate denuclearization. The is the first time the U.S. has seized a North Korean ship for sanctions violations and U.S. officials say it is part of a broader push to increase pressure on Pyongyang to dismantle its nuclear program. The coal sector is key to the North Korean economy and its nuclear weapons program. The ship, named Wise Honest, was also importing heavy machinery.

The Wise Honest was first stopped in April 2018 in Indonesia when authorities there detained the vessel after it was photographed at a North Korean port. “Experts have said that to evade sanctions, North Korea conducts its illicit trading with a fleet of ghost ships that have false names painted on their hulls, steal identification numbers from other vessels and execute their trades via ship-to-ship transfers at sea to avoid prying eyes at ports,” the Washington Post reports. “In the case of the Wise Honest, a globe-trotting North Korean salesman arranged the 2018 shipment by holding meetings at North Korea’s embassy in Jakarta, then paid an Indonesian broker through bank transfers facilitated by JPMorgan Chase, according to bank documents and other evidence gathered by sanctions monitors.”

During its voyage to Indonesia, the carrier ship traveled with a deactivated Automatic Identification System, concealing details about its identity, cargo, and destination. The ID system had been turned off for more than a year. “Three American banks were unwittingly ensnared in the scheme, officials said, transmitting payments around the world for maintenance, equipment and improvement of the shipping vessel,” the New York Times reports. “The Justice Department seized the vessel from the Indonesians, and the United States Coast Guard evaluated it to ensure it was safe enough to make the trip [to U.S. territory], a spokeswoman said. The vessel is being towed by a commercial tow boat to American Samoa, officials said.”