“If they’re co-belligerents, their intention is to participate in this war on Russia’s behalf, that is a very, very serious issue, and it will have impacts not only in Europe, it will also impact things in the Indo-Pacific,” he said.

The US confirmation comes after South Korea’s spy agency last week announced that North Korea sent 1,500 troops to support Russia’s war against Ukraine.

The country’s National Intelligence Service (NIS) said that Russian navy ships transferred the soldiers to the port city of Vladivostok from October 8 to October 13.

The NIS said the soldiers were given Russian military uniforms, weapons and forged identification documents.

The agency posted satellite images showing Russian navy ship movements near a North Korean port and suspected North Korean mass gatherings in Ussuriysk and Khabarovsk in the past week.

Ukrainian President Volodymyr Zelensky said his government has intelligence that 10,000 troops from North Korea are being prepared to join Russian forces.

“From our intelligence we’ve got information that North Korea sent tactical personnel and officers to Ukraine,” Zelensky said.

Zelensky warned that a third nation wading into the hostilities could turn the conflict into a “world war.”

Earlier this week, Vice South Korean Foreign Minister Kim Hong Kyun spoke to his Russian counterpart and demanded the immediate withdrawal of North Korean troops in Russia.

He said the troop dispatch was “a grave security threat” to South Korea and the international community.

Russia has previously denied using North Korean troops in the war.

Ukrainian media reported earlier this month that six North Koreans were among those killed after a Ukrainian missile strike in the Donetsk region.