LONDON (AP) — Armed British forces boarded and detained a sanctioned tanker Sunday that is suspected of being part of the Russian "shadow fleet," shipping oil in violation of international sanctions over Moscow's war on Ukraine, British Prime Minister Keir Starmer said Sunday.

Royal Marine commandos rappelled from helicopters onto the vessel, the Smyrtos, in the English Channel, in what the country's Defense Ministry called "the first U.K.-led operation of its kind."

The vessel will be held and monitored off the south coast of England for investigation, according to the Defense Ministry. The operation was carried out "in close coordination" with French authorities, who have previously intercepted a number of vessels linked to the "shadow fleet."

"This operation delivers yet another blow to Russia and reminds those fueling Putin's war in Ukraine that they cannot hide," Starmer said.

Russia is believed to be using a fleet of hundreds of ships to evade sanctions over its war against Ukraine.

Sailing under a Cameroon flag, the Smyrtos left the Russian Baltic port of Ust-Luga on June 5 destined for Port Said, Egypt, according to the MarineTraffic website.

U.K. authorities said that such operations were "directly bearing down on the resources sustaining Russia's aggression in Ukraine and reducing its capacity to threaten security across Europe and beyond."

Ukraine President Voldymyr Zelenskyy thanked Starmer and the British people for their "principled resolve."

"It was Russia's hubris, fueled by high oil and gas revenues, that paved the way for this war, and every decision by partners that deprives Russia of money also limits the war itself," Zelenskyy said on X.

"Europe urgently needs to take legislative steps to enable not only the detention of tankers and restrictions on oil shipments, but also the confiscation of the oil they carry."