Seoul "will not stand by but respond firmly in collaboration with the international community," South Korea said.

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.

Defense Secretary Lloyd Austin said the U.S.has evidence North Korea has sent military forces to Russia, affirming accusations made by Ukraine and South Korea.