North Korea has sent troops to Russia to support Moscow’s war in Ukraine, the United States said Wednesday, a major escalation in the conflict that has rattled Western allies.

North Korea’s supply of munitions has already been critical to the Russian war effort. Now, there are growing fears that it is sending troops as well.

Secretary of Defense Lloyd Austin said North Korea has deployed troops to Russia, the first senior US official to confirm the development on the record, as North Korea and Russia have forged increasingly friendly ties since Moscow’s invasion of Ukraine.