The Biden administration and its European and Asian allies find themselves fighting an information war against both Russia and China as President Vladimir V. Putin of Russia continues his military onslaught in Ukraine.

The Chinese government’s promotion of Russian disinformation in the middle of the war has ignited concern among Western officials because of China’s powerful diplomatic standing and extensive cyberabilities. Analysts who study disinformation from the two nations said this was the first time they had seen this scale of amplification between Beijing and Moscow around a conspiracy theory.

“I can’t think of another active propaganda campaign by Russia that has gotten this level of boost from China,” said Bret Schafer, who tracks disinformation from China, Russia and Iran as a senior fellow for the Alliance for Securing Democracy, a Washington nonprofit group. “I haven’t seen this volume around something like this.”