WASHINGTON (Reuters) -China is backing Russia's war effort in Ukraine by helping Moscow in its biggest military buildup since the Soviet era, providing drone and missile technology, satellite imagery and machine tools, senior U.S. officials said on Friday. However, the Chinese Embassy in the U.S. said it has not provided weaponry to any party, adding that it is "not a producer of or party involved in the Ukraine crisis." The officials, speaking on condition of anonymity, said U.S. President Joe Biden raised the issue with Chinese President Xi Jinping in their recent phone call and that it is a topic of discussion with U.S. allies in Europe and around the world.