South Korea’s spy chief has told lawmakers that North Korea has sent another 1,500 troops to Russia to support its war against Ukraine.

Secretary of Defense Lloyd J. Austin III confirmed on Wednesday that North Korea had sent troops to Russia to join the fight against Ukraine, a major shift in Moscow’s effort to win the war. Mr. Austin called the North’s presence a “very serious” escalation that would have ramifications in both Europe and Asia.

The United States said for the first time on Wednesday that it had seen evidence that North Korea has sent 3,000 troops to Russia for possible deployment in Ukraine, a move that could mark a significant escalation in Russia's war against its neighbor.