China, with which Trump is trying to negotiate a resolution to various trade issues after a painful tariff war, is Russia's biggest oil customer. Beijing's large-scale oil purchases have aided Russia through the Western sanctions over the Ukraine war, offering a vital economic lifeline.

U.S. and European officials have met at the U.S. Treasury Department to discuss economic pressure on Russia, including new sanctions and tariffs on Russian oil

Donald Trump has threatened tougher sanctions against Russia after its heaviest aerial bombardment on Ukraine since the war began. Sunday's strikes killed four people, including a mother and her baby,