LONDON (AP) — Britain sanctioned 30 ships in Russia's so-called shadow fleet that have been skirting restrictions to transport billions of dollars of petroleum, the Foreign Office said Monday.

It is the biggest sanctions package targeting the fleet of illegitimate and often decrepit ships that are operating illegally to avoid sanctions, the Foreign Office said. The U.K. has now sanctioned 73 tankers, the most of any nation, in efforts to cripple a major funding source for Moscow’s war against Ukraine.

“Russia’s oil revenues are fueling the fires of war and destruction in Ukraine,” Foreign Secretary David Lammy said in Italy at a meeting of G7 foreign ministers. “We are determined to ensure that both the ships and the enablers of those ships thwarting European and U.K. sanctions are hurt at this time.”

Half the ships sanctioned delivered more than 3.4 billion pounds ($4.3 billion) worth of oil and oil products in the past 12 months, a Foreign Office statement said. Two insurers were sanctioned for enabling the fleet.

Leaders at the European Political Community summit in July had agreed to tighten sanctions on the fleet.