Washington DC - The White House on Friday responded sarcastically to Vladimir Putin exchanging a hug with Xi Jinping on a visit to Beijing as Russia and China continue to grow closer.

"Exchanging hugs? Well, that's nice for them," National Security Council spokesperson John Kirby told a briefing when asked about the significance of photos showing the two US adversaries locked in an embrace.

"I'm not good at talking about personal human bodily affection one way or the other. I think I'll leave it to these two gents to talk about why they thought it was good to hug one another," said Kirby, a naval admiral known for his dry remarks from the podium.

The US has repeatedly voiced concerns about Chinese companies supplying Russia with technology for its invasion of Ukraine.

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But Kirby said Putin's visit did not seem to have secured any major advances in this regard, and Washington had not seen Xi "rush" to assist Moscow's armed forces.

"We didn’t see anything coming out of this meeting that we were necessarily surprised by," he said.

But he added that "I wouldn't go so far as to say we weren't concerned about this relationship and where it's going. We're watching."

Putin arrived Thursday on his first trip abroad since his March re-election, meeting Xi for talks in which the leaders framed their nations' ties as a stabilizing force in a chaotic world.