House intel chair: US should consider military action if North Korean troops enter Ukraine

More: North Korean shock troops in Ukraine? South Korea summons Russian ambassador over reports.

North Korean troops are 'legitimate military targets,' White House says

If they join the fight in Ukraine, North Korean troops "will become legitimate military targets," White House National Security Council Spokesperson John Kirby told reporters at the White House on Wednesday.

Kirby said the U.S. believes North Korea sent at least 3,000 troops by boat to Vladivostok, a city on the far eastern coast of Russia. The soldiers then moved to multiple military bases in Russia's eastern region.

"We do not yet know whether these soldiers will enter into combat alongside the Russian military, but this is certainly a highly concerning probability," he said. "After completing training, these soldiers could travel to western Russia and then engage in combat against the Ukrainian military."

South Korean President Yoon Suk Yeol and Polish President Andrzej Duda condemned the reported deployment during a summit on Thursday.

"We agreed that North Korea's dispatch of troops to Russia is a direct violation of U.N. Security Council resolutions and the U.N. Charter and is a provocation that goes beyond the Korean Peninsula and Europe to threaten global security," Yoon said.

Seoul consulted with the U.S. about the alleged deployment on Monday. Kim Hong-kyun, the South Korean vice foreign minister, summoned the Russian ambassador the same day to condemn the "illegal military cooperation," which he called a violation of international law and a threat to South Korea's security interests, according to a statement released by the foreign ministry.

"We will respond jointly with the international community by mobilizing all available means against acts that threaten our core security interests," he said.

South Korean lawmakers said on Wednesday that 3,000 North Korean troops were believed to be in Russia, a number double the estimate the South Korean Intelligence Service said it identified last week. The spy agency said it worked with Ukraine's spies and used facial recognition technology and artificial intelligence to track North Korean military officers in Russia.

The Kremlin has denied the reports, branding them "fake news." A North Korean United Nations representative called them "groundless rumors" at a Monday meeting.

North Korean leader Kim Jong Un has tightened ties with Russian President Vladimir Putin since the war in Ukraine began. In a rare trip to North Korea in June, Putin signed a diplomatic with defense pact with Kim, and Kim expressed his support for the invasion of Ukraine.

North Korea has already provided large artillery shells to Russia's war effort.

Cybele Mayes-Osterman is a breaking news reporter for USA Today. Reach her on email at cmayesosterman@usatoday.com. Follow her on X @CybeleMO.