British armed forces boarded a Russian shadow fleet oil tanker in the English Channel in the early hours of Sunday morning, Sir Keir Starmer has said.
In an operation lasting six hours, Royal Marine Commandos and specially trained law enforcement officers from the National Crime Agency intercepted the vessel and, for the first time, boarded it, supported by the RAF.
The vessel, Smyrtos, will be held and monitored off the south coast of England as investigations continue, the MoD said in a statement.
Sir Keir Starmer said: "This successful operation delivers yet another blow to Russia and reminds those fuelling Putin's war in Ukraine that we will not let them hide."
According to tracking website MarineTraffic, Smyrtos sails under a Cameroon flag and is at anchor off the coast of Weymouth in the English Channel.
It began its journey on 5 June from Russia's Ust-Luga port, an oil terminal near St. Petersburg, before crossing west into the channel on Saturday, BBC Verify has found.
The vessel was sanctioned in July 2025 and has since changed its name from Myrtos to Smyrtos as well as the flag it sails under twice.
Russia has been operating a "shadow fleet" of tankers to evade international sanctions imposed on its oil exports.