The US is "confident" that China is seriously considering providing weapons to back the Russian forces invading Ukraine, said CIA Director William Burns.
Any such step by China would be "a very risky and unwise bet”, the intelligence chief told CBS on Sunday.
His comments, along with others on Sunday by National Security Adviser Jake Sullivan, constituted the latest US warning to China against providing weapons.
But Mr Burns and Mr Sullivan made it clear that the US has not yet detected signs that any arms have been shipped.
"We actually haven't seen them take a final decision … and we haven't seen the aid be provided to Russia," Mr Sullivan told CNN.
US officials quoted by The Wall Street Journal say China is considering sending drones and munitions to Russia. China has denied the claims.
With the conflict in its second year, Mr Burns said Russian President Vladimir Putin was nowhere near ready to engage in serious peace talks.
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"I think Putin is, right now, entirely too confident of his ability … to wear down Ukraine, to grind away," he said.
But at some point, Mr Burns said, the Russian leader was "going to have to face up to the increasing costs as well, in coffins coming home" and in "cumulative economic damage”.
As the war drags on, US officials have increased their warnings to Beijing that delivering lethal weapons to Moscow could have profound consequences.
US President Joe Biden said on Friday that he did not "anticipate a major initiative" from China to provide weapons to Russia.
But his comments came days after Secretary of State Antony Blinken said China was "considering providing lethal support”.
Mr Biden said he previously told Chinese President Xi Jinping that a move to arm Russia would have dire economic repercussions.
"Without any government prodding, 600 American corporations left Russia, from McDonald's to Exxon," he said he told Mr Xi.
Agence France-Presse contributed to this report
