United Nations Secretary-General António Guterres said he is “very concerned” about reports that North Korea has deployed troops to Russia and that some may soon join the front lines of the war with Ukraine.

In a statement issued Sunday, Guterres’ spokesperson Stephane Dujarric said the UN chief believes the deployment of North Korean troops would be a “very dangerous escalation” of the war in Ukraine.

Calling for steps to prevent the internationalization of the conflict, Guterres urged “meaningful efforts” to end the war.

The U.S. government estimated in late October that around eight-thousand North Korean soldiers had been dispatched to Russia’s Kursk region, near the border, and could enter conflict zones in the coming days.

The Ukrainian military claimed that some seven-thousand North Korean soldiers were stationed along the border as of late last month.

It said the North Koreans were armed with 60-millimeter mortars, night vision goggles and anti-tank guided missiles.