WASHINGTON — Russia asked China to give it military equipment and support for the war in Ukraine after President Vladimir V. Putin began a full-scale invasion last month, according to U.S. officials.

Russia has also asked China for additional economic assistance, to help counteract the battering its economy has taken from broad sanctions imposed by the United States and European and Asian nations, according to an official.

American officials, determined to keep secret their means of collecting the intelligence on Russia’s requests, declined to describe further the kind of military equipment Moscow is seeking. The officials also declined to discuss any reaction by China to the requests.

President Xi Jinping of China has strengthened a partnership with Mr. Putin and has stood by him as Russia has stepped up its military campaign, destroying cities in Ukraine and killing hundreds or thousands of civilians. American officials are watching China closely to see whether it will act on any requests of aid from Russia. Jake Sullivan, the White House national security adviser, is scheduled to meet on Monday in Rome with Yang Jiechi, a member of the Chinese Communist Party’s elite Politburo and director of the party’s Central Foreign Affairs Commission.

Mr. Sullivan intends to warn Mr. Yang about any future Chinese efforts to bolster Russia in its war or undercut Ukraine, the United States and their partners.

“We are communicating directly, privately to Beijing, that there will absolutely be consequences for large-scale sanctions evasion efforts or support to Russia to backfill them,” Mr. Sullivan said on CNN on Sunday.

“We will not allow that to go forward and allow there to be a lifeline to Russia from these economic sanctions from any country, anywhere in the world,” he said.

Mr. Sullivan did not make any explicit mention of potential military support from China, but other U.S. officials spoke about the request from Russia on the condition of anonymity because of the sensitivity of diplomatic and intelligence matters.

The Biden administration is hoping to convince the Chinese to pressure Mr. Putin to change his course in Ukraine, something many current and former officials believe is unlikely. But some in the administration believe it could be possible to dissuade China from stepping up its assistance to Moscow. Beijing may be content to offer rhetorical support for Moscow, and not want to involve itself further on Russia’s side by providing military equipment to assist in the invasion of Ukraine.

Mr. Sullivan said China “was aware before the invasion took place that Putin was planning something,” but added that Mr. Xi or his aides might not have been aware of the full extent of the Russian leader’s plans. “It’s very possible that Putin lied to them in the same way he lied to Europeans and others,” he said.