Britain’s armed forces have for the first time intercepted and seized control of a Russian shadow fleet oil tanker sailing in the English Channel, the British Defense Ministry said on Sunday.

Royal Marine Commandos and specially trained law enforcement officers boarded the vessel early Sunday in a military operation that lasted six hours and that was supported by British military ships and aircraft, the ministry said in a statement.

The intercepted tanker, the Smyrtos, will be held and monitored off the southern coast of England, the ministry added.

“This operation delivers yet another blow to Russia and reminds those fueling Putin’s war in Ukraine that they cannot hide,” Prime Minister Keir Starmer of Britain said in a statement, referring to President Vladimir V. Putin of Russia.

Russia’s shadow fleet is a collection of often dilapidated ships with hazy ownership that covertly moves fuel around the globe, enabling the country to sidestep international sanctions imposed after its invasion of Ukraine.

According to the British government, the shadow fleet consists of more than 700 vessels and is responsible for carrying 75 percent of Russia’s sanctioned oil, giving the Kremlin an important economic lifeline.