WASHINGTON/MOSCOW (Reuters) - The United States on Thursday imposed sanctions on a firm it said was participating in a scheme to avoid U.S. sanctions while helping provide jet fuel to Russian forces in Syria.

The U.S. Treasury Department said the newly sanctioned firm, Maritime Assistance LLC, was operating as a front company for OJSC Sovfracht, a Russian company the United States had previously sanctioned in relation to operations in Ukraine.

The Treasury also targeted three individuals it said were tied to Sovfracht, freezing any assets they may hold in the United States and barring Americans from dealing with them.

Five ships were also designated as “blocked property” of previously sanctioned Russian firm Transpetrochart, which Washington alleges provides support to Sovfracht.

The United States accuses Sovfracht of being behind a sanctions-evasion conspiracy to make payments and facilitate the transfer of supplies of jet fuel to Russian forces operating in Syria in support of the government of President Bashar al-Assad.

Moscow launched its campaign in Syria in 2015, helping its close ally Assad turn the tide in the conflict.

Russia’s foreign ministry criticized the new U.S. sanctions in a statement on Friday and said that by seeking to undermine the Russian military’s refueling efforts in Syria, Washington was effectively siding with radical militants there.