Britain imposed new sanctions on Russian oil majors Gazprom Neft and Surgutneftegaz on Friday, in a move co-ordinated with the United States.
"Oil revenues are the lifeblood of (Russian President Vladimir) Putin's war economy," foreign minister David Lammy said in a statement. "Taking on Russian oil companies will drain Russia's war chest."
Britain and its Western allies have also been targeting the so-called shadow fleet in response to Russia's invasion of Ukraine, saying that the vessels trade in illicit Russian oil that helps fund Putin's war effort.