U.S. says North Korea has sent troops to Russia for training NPRChina May Chafe as North Korea Sends Soldiers to Fight Ukraine The New York TimesNorth Korean troops in Ukraine ‘fair game’, US warns Russia as war rages on Al Jazeera EnglishKey Republican: US should consider ‘direct military action’ if North Korean troops enter Ukraine The HillNorth Korean troops are in Russia, would be ‘legitimate targets’ in Ukraine, U.S. says The Washington Post