The U.S. State Department said it was concerned by North Korea's direct involvement in Russia's war in Ukraine and that Pyongyang's military deployment for Russia must end.

"We continue to be concerned by (North Korea's) direct involvement in the war. (North Korea's) military deployment to Russia and any support provided by the Russian Federation to (North Korea) in return must end," a State Department spokesperson said in an email, adding third countries like North Korea "bear responsibility" for the war.

North Korea confirmed for the first time on Monday that it has sent troops to fight for Russia in the war with Ukraine under the order of leader Kim Jong Un.