White House Press Secretary Karoline Leavitt said Wednesday that the Trump administration will continue to enforce an embargo against all "shadow fleet" vessels alleged by the U.S. to illegally transport oil, reported Xinhua. Leavitt made the remarks hours after the U.S. Coast Guard seized two Venezuela-linked oil tankers in the Atlantic and the Caribbean on Wednesday morning. U.S. Southern Command on X described the second vessel seized in the Caribbean Sea, the Sophia, as a "stateless, sanctioned dark fleet" ship that was "conducting illicit activities." It said the U.S. Coast Guard is escorting the vessel to the United States for "final disposition." Leavitt also accused the Russia-flagged Marinera vessel, previously known as the Bella 1, which was seized first on Wednesday morning by U.S. forces in the North Atlantic, of being part of a "Venezuelan shadow fleet" that transported sanctioned oil. Shortly after the U.S. seizure of the Marinera, the Russian Foreign Ministry demanded a "speedy return" of Russians on board. "Considering the incoming information regarding the presence of Russian citizens among the crew, we demand that the American side ensure their humane and dignified treatment, strictly respect their rights and interests, and not impede their speedy return to their homeland," TASS news agency quoted the ministry as saying. The Russian Transport Ministry said Wednesday the vessel was granted temporary authorization on Dec. 24, 2025 to sail under the Russian state flag in accordance with Russian legislation and international law. "In accordance with the 1982 UN Convention on the Law of the Sea, freedom of navigation applies in waters on the high seas, and no state has the right to use force against vessels duly registered under the jurisdiction of other states," the ministry said in a statement. As of Wednesday, U.S. forces have seized four oil tankers linked with Venezuela. On Dec. 10, U.S. forces seized the oil tanker Skipper near Venezuelan waters and announced U.S. plans to keep its oil cargo. Ten days later, the U.S. Coast Guard boarded the Centuries vessel off Venezuela, a Panamanian-flagged supertanker that was not on Washington's sanctions list. White House spokesperson Anna Kelly said on X that the crude oil aboard the Centuries originated from Venezuela's state-owned oil company Petroleos de Venezuela SA, which is under U.S. sanctions. U.S. President Donald Trump ordered a "total and complete blockade" of all sanctioned tankers entering or leaving Venezuela last month. The United States launched a large-scale military operation against Venezuela in the early hours of Jan. 3, taking by force Venezuelan President Nicolas Maduro and his wife, before putting them in custody in New York. The strikes have drawn worldwide condemnation and concern. Later that day, Trump said he planned to authorize U.S. oil giants to take over and invest in Venezuela's energy infrastructure and "start making money for the country," adding that the embargo on all Venezuelan oil "remains in full effect."