Putin’s admission of Chinese concerns about Ukraine isn’t a sign of a weakening bond, U.S. officials said.

China’s quiet ambivalence about aspects of Russia’s war in Ukraine has long been understood by Moscow, but ties between the two countries remain strong — even if it was notable that President Vladimir V. Putin acknowledged Beijing’s concerns publicly, American officials said Thursday.

“What’s striking is Putin’s admission that President Xi has concerns about Russia’s war against Ukraine,” Ned Price, the State Department spokesman, said a few hours after the two leaders met in Uzbekistan. Those concerns shouldn’t be a surprise, he said, but added: “It is somewhat curious that President Putin would be the one to admit it.”

Mr. Putin appears to have felt that publicly acknowledging China’s concerns would send a reassuring message to it and other countries that support Moscow, according to U.S. officials.

But there is little chance of any sort of break between Mr. Putin and Mr. Xi.

Fundamentally, both leaders want to challenge the power of the United States and its allies, and each sees the other as a useful weapon against American influence in the international order. Some U.S. analysts say Mr. Xi and Mr. Putin see similarities between Russia’s ambitions in Ukraine and China’s view of Taiwan.

“We’ve made clear our concerns about the depth of China’s alignment and ties with Russia — even as Russia prosecutes a war of aggression in Ukraine,” Mr. Price’s office said in a statement. “This meeting is an example of that alignment.”

While a declaration by the two nations in February announced a partnership with “no limits,” U.S. officials have insisted for months that Mr. Putin is keenly aware of the relationship’s real-world boundaries.

Mr. Price said that the U.S. government assesses that Russia still seeks material aid from China for the war in Ukraine. Unable to buy weaponry or parts from China, Russia has in recent months turned to Iran for drones and North Korea for rockets and artillery rounds, according to U.S. officials.

Multiple U.S. officials said that so far China has not provided any military assistance — and does not seem poised to change that policy.

While Beijing is willing to buy oil from Russia at below-market prices and to provide rhetorical support for Moscow, as well as help Moscow spread disinformation about the Ukraine war, China believes any direct military support would lead to sanctions and export controls that would damage the Chinese economy at a fragile time, U.S. officials say.

But Mr. Xi still wants the benefits of a partnership, according to American officials. And Mr. Putin believes Beijing would need Russian help if a military conflict broke out between China and Taiwan, the officials say, which means Mr. Xi will maintain the partnership even if he has concerns over how the war in Ukraine is going.

Some former officials believe Mr. Putin’s comments may have been inspired by earlier back-channel discussions between Moscow and China. But it is not clear whether any such direct communication is necessary.

U.S. officials have said Mr. Putin has surely known about China’s concerns since the beginning of the invasion, when Russia failed to quickly take Kyiv and Moscow faced swift and severe international condemnation.

A Western intelligence report said that Chinese officials asked Russian officials in early February to delay an invasion of Ukraine until after the Winter Olympics in Beijing, U.S. and European officials said in March. Mr. Putin announced he was sending additional Russian forces into eastern Ukraine, which had been under siege since 2014 by a Russian-backed insurgency, the day after the Olympics ended.