"I've been hearing now for the past three months (that) China is going to provide significant weapons to Russia... They haven't yet. Doesn't mean they won't, but they haven't yet," he told a news conference during a visit to Canada.

"I don't take China lightly. I don't take Russia lightly," he added, while also suggesting that reports of their rapprochement had probably been "exaggerated."

Conversely, Biden stressed the strong ties among Western democracies, saying "if anything's happened, the West has coalesced significantly more."

He pointed to US security alliances in the Pacific region such as the Quad which also includes Australia, India and Japan and as well as AUKUS with Australia and Britain.

During a visit by Chinese President Xi Jinping to Moscow this week, Russia and Beijing for their part hailed "the special nature" of their relations.

But while China's leader pledged a trade lifeline and some moral support, more conspicuous was that he did not commit to providing arms for Russia's depleted forces in Ukraine, a move that would have invited Western sanctions on China.

There was also no long-term Chinese commitment to buy vast quantities of Russian gas that is no longer flowing to Europe.