March 26 (UPI) — Britain’s armed forces and law enforcement have been authorized to board sanctioned vessels of Russia’s so-called shadow fleet, Prime Minister Keir Starmer announced Wednesday, as London targets a key revenue source funding the Kremlin’s war against Ukraine.

In an effort to hinder Russian President Vladimir Putin’s ability to wage war, Britain, along with other European nations, has focused on his fleet of semi-clandestine tankers used to evade sanctions to ship and sell oil.

London has sanctioned at least 544 of these ships and the EU has blacklisted nearly 600.

Russia’s shadow fleet is estimated to consist of anywhere from several hundred to more than 1,000 vessels, according to the Center for Strategic and International Studies. In September, this fleet transported a seasonal high of 3.7 million barrels of oil a day, real-time intelligence, analytics and data-tracking firm Kpler said.

Britain’s armed forces will be able to interdict vessels London has sanctioned and found transiting its waters, Starmer said a day before he is to arrive at the Joint Expeditionary Force Summit in Helsinki, Finland, where leaders will discuss regional security amid the U.S.-Israel war with Iran and how they can combat Russia’s escalating aggression.

“Putin is rubbing his hands at the war in the Middle East because he thinks higher oil prices will let him line his pockets,” Starmer said in a statement.

“That’s why we’re going after his shadow fleet even harder, not just keeping Britain safe but starving Putin’s war machine of the dirty profits that fund his barbaric campaign in Ukraine.”

According to 10 Downing Street, a suspect vessel will first be reviewed by law enforcement, military and energy specialists, who will then make a recommendation to ministers before an operation is carried out.

After the ship is detained, criminal proceedings may be brought against the vessel’s owners, operators and crew on allegations of breaching British sanctions, it said.

Starmer said that Putin and those in his inner circle “should be in no doubt: We will always defend our sovereignty and stand with Ukraine for as long as it takes.”

The announcement comes months after Britain aided the United States in seizing Bella 1 on Jan. 7. Following the operation, British ministers ordered the development of plans for London to carry out future, similar operations targeting Russia’s shadow fleet, resulting in Wednesday’s announcement, according to 10 Downing Street.