LONDON — British authorities have detained a tanker suspected of being part of Russia’s so-called “shadow fleet” in what officials described as the United Kingdom’s first direct action against a vessel linked to sanctioned Russian oil trade.

The tanker, identified as Smyrtos, was intercepted in the English Channel on June 14 during a coordinated operation involving Royal Marine Commandos, law enforcement personnel, military aircraft, and Royal Navy vessels. Authorities reported that the boarding was carried out without resistance from the crew.

According to British officials, the vessel is suspected of transporting Russian oil in ways that may breach international sanctions imposed over the conflict in Ukraine. Reports indicated that the tanker was sailing under a Cameroonian flag and had departed from a Russian oil terminal before entering waters near the United Kingdom.

Following the operation, investigators from the UK’s National Crime Agency began examining the vessel’s records, documents, and onboard systems as part of an ongoing inquiry. Authorities said the tanker would remain under monitoring while the investigation continues.

British Prime Minister Keir Starmer said the operation reflects the country’s efforts to enforce sanctions and address activities that may support Russia’s oil trade. Ukrainian President Volodymyr Zelenskyy also welcomed the action and called for continued international cooperation in preventing sanctions evasion.