Britain on Monday slapped sanctions on 135 oil tankers in Russia’s shadow fleet in a bid to disrupt the flow of money helping Moscow fund the war in Ukraine.

A shipping services company and an oil trading firm were also sanctioned as part of the crackdown on a fleet “responsible for illicitly carrying $24 billion worth of cargo since the start of 2024,” the Foreign Office said in a statement.

Security analysts say the fleet of aging vessels is used by Russia to circumvent international sanctions that ban it from selling oil.

Hundreds of vessels have now been sanctioned by the European Union and the U.K. since Russian President Vladimir Putin ordered the invasion of Ukraine in February 2022.