Russia has asked China for military support, including drones, as well as economic assistance for its unprovoked invasion of Ukraine, according to conversations CNN had with two US officials, the news agency reported.

The requests came after Russia's invasion of Ukraine, one of the officials said. That official declined to detail the Chinese reaction, but indicated that the Chinese had responded.

When asked by CNN about the reporting of Russia's request for military aid, Liu Pengyu, spokesperson for the Chinese embassy in the US, said in a statement, "I've never heard of that."

Liu expressed concern for "the Ukraine situation"—calling it "indeed disconcerting"—, and said China has and will continue to provide humanitarian assistance to Ukraine.

Liu said: "The high priority now is to prevent the tense situation from escalating or even getting out of control. ... China calls for exercising utmost restraint and preventing a massive humanitarian crisis."

News of Russia's request comes before White House national security adviser Jake Sullivan will meet with his Chinese counterpart, Yang Jiechi, in Rome on Monday.

Sullivan told CNN on Sunday that China providing Russia with support is a "concern."

"We also are watching closely to see the extent to which China actually does provide any form of support, material support or economic support, to Russia. It is a concern of ours. And we have communicated to Beijing that we will not stand by and allow any country to compensate Russia for its losses from the economic sanctions," Sullivan said.

Sullivan added that the US has made it clear to Beijing that there will "absolutely be consequences" for "large-scale" efforts to give the Kremlin a workaround to US sanctions.