Russia's invasion of Ukraine has made it more of a strategic burden on China, a senior Pentagon official said on Thursday.

"I do think that there's a degree to which what Putin has done in Ukraine makes Russia much more of a strategic burden for Beijing than it was six weeks ago or six months ago," Under Secretary of Defense for Policy Colin Kahl said.

In February, China and Russia declared a "no limits" partnership, backing each other over standoffs on Ukraine and Taiwan with a promise to collaborate more against the West.