“Beijing will have to make its own decisions about how it proceeds, whether it provides military assistance, but if it goes down that road, it will come at real costs to China,” Sullivan said in an interview with CNN’s “State of the Union” programme.

China has not moved forward in providing that aid, but neither has Beijing taken that option off the table, Sullivan said in a separate interview on ABC’s “This Week” programme.

US officials have warned their Chinese counterparts behind closed doors about what those costs might be, Sullivan said, but he would not elaborate on those private discussions.

The US and its Nato allies have been scrambling to warn China against such a move in recent days, making public comments on their belief that China is considering providing lethal equipment to Russia.

CIA director William Burns also weighed in regarding China today.

“We’re confident that the Chinese leadership is considering the provision of lethal equipment. We also don’t see that a final decision has been made yet, and we don’t see evidence of actual shipments of lethal equipment,” Burns told the CBS programme “Face the Nation.”

Republican representative Michael McCaul, chairman of the House of Representatives foreign affairs committee, said on “This Week” that the US intelligence shows drones are among the lethal weapons China has considered sending to Russia.

US president Joe Biden visited Kyiv and met with President Volodymyr Zelensky last Monday, promising new military aid for Ukraine worth US$500 million. Last week marked the first anniversary of Russia’s invasion. The US has been by far the largest supplier of military assistance to help Ukraine repel better-equipped Russian forces. Ukraine expects a major new Russian offensive soon.