Defense chief Lloyd Austin says the U.S. sees evidence that Kim Jong Un has sent troops to bolster Vladimir Putin's army amid the ongoing invasion of 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.

Reports that the North is sending troops to Russia stoked security jitters in South Korea. It has shipped humanitarian and financial support to Ukraine, but it has so far avoided directly supplying arms in line with its policy of not supplying weapons to countries actively engaged in conflicts.