White House national security adviser Jake Sullivan said on Sunday that China has not taken any steps toward offering deadly assistance that would aid Russia in its invasion of Ukraine and that the United States has made it plain behind closed doors that such a move would have catastrophic repercussions.

Sullivan stated this in an interview with CNN’s “State of the Union” program: “Beijing will have to make its own decisions about how it continues, whether it gives military help, but if it goes down that road, it will come at serious costs to China.”

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” program.

U.S. 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 United States 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 on Sunday.

“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 program “Face the Nation.”

Republican Representative Michael McCaul, chairman of the House of Representatives Foreign Affairs Committee, said on “This Week” that the U.S. intelligence shows drones are among the lethal weapons China has considered sending to Russia.

In a meeting with President Volodymyr Zelenskiy last Monday, U.S. Vice President Joe Biden pledged $500 million in fresh military assistance for Ukraine. The first anniversary of Russia’s invasion was last week. By far, the main provider of military aid to Ukraine in its efforts to fend off better-equipped Russian soldiers has been the United States. Ukraine anticipates an imminent large new Russian attack.