The United States said China will face harsh “consequences” if it aids Russia in its invasion of Ukraine, according to media reports.
Multiple US news outlets reported that Russia asked China to provide military assistance after it began the invasion.
The Chinese foreign ministry described the allegation as disinformation from the US.
The exchanges come as top US and China officials prepare to meet in Rome.
US media outlets, citing Washington officials, say that Russia has in recent days asked China specifically for military equipment, including drones.
In a CNN interview, US National Security Adviser Jake Sullivan said they were “communicating directly, privately to Beijing that there will absolutely be consequences for large-scale sanctions evasion efforts or support to Russia to backfill them”.
“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.
He added that while the US believed China was aware that Russian leader Vladimir Putin was “planning something” before the invasion happened, Beijing “may not have understood the full extent of it”.
“Because it’s very possible that [Mr] Putin lied to them the same way that he lied to Europeans and others,” Mr Sullivan said.
In response, a spokesman for the foreign ministry in Beijing, Zhao Lijian, said the US was spreading disinformation.
He added that China’s stance had always been consistent and that China was playing a constructive role in promoting talks.
Mr Sullivan is due to meet Yang Jiechi, a member of China’s top decision-making body, the Politburo, and the head of the Central Foreign Affairs Commission, on Monday in Rome.
Reuters reported that during the meeting Mr Sullivan would spell out the consequences and isolation China would face if it increased support for Russia.
China has so far refrained from condemning Russia for the invasion and has said Moscow’s “legitimate security concerns” should be taken seriously.
But Beijing at the same time has expressed “unwavering support” for Ukraine’s sovereignty. It has also called for peace and has said it is ready to help end the war through diplomacy. Several countries have urged China to do more to stop Russia’s invasion.