The United States warned Tuesday that it will hold China responsible if Moscow makes gains in Ukraine, after Beijing renewed pledges of cooperation during a visit by Russia's top diplomat.

Kurt Campbell, the deputy secretary of state long associated with regearing US policy toward Asia, said that for the United States, maintaining peace and stability in Europe is "our most important mission historically."

With Moscow renewing its Ukraine offensive amid a deadlock in the US Congress on approving more weapons to Ukraine, Campbell warned that Russian territorial gains could "alter the balance of power in Europe in ways that are, frankly, unacceptable."

"We have told China directly, if this continues, it will have an impact on the US-China relationship. We will not sit by and say everything is fine," Campbell said.

"We will see this not as just a Russian unique set of activities but a conjoined set of activities backed by China but also North Korea. This is antithetical to our interests," he told the National Committee on US-China Relations, an educational group.

Campbell was responding to a question about a visit Tuesday by Russian Foreign Minister Sergei Lavrov to China, where President Xi Jinping told him that Beijing was ready to strengthen coordination.

Campbell said that President Joe Biden's administration had warned Chinese officials in advance of intelligence indicating Russian President Vladimir Putin would order an invasion of Ukraine in February 2022.

"I'm not sure they completely believed us, or thought that maybe it would be a smaller thing, not an all-out move and push," Campbell said.

Campbell said China was alarmed to see Russia's early setbacks and worked to rebuild a "whole variety of capacities" for Moscow.

"Initially, that was a defensive endeavor. They did not want to see regime change," Campbell said.

But more than two years later, "Russia has almost completely retooled, and they now pose a significant threat going forward to Ukraine (and) to the surrounding region," Campbell said.

The United States has repeatedly threatened sanctions if China takes more substantial action to support Russia.

US officials say that Russia has increasingly turned to arms from North Korea and Iran, both under heavy sanctions, to fuel its war in Ukraine.