A high-level delegation from South Korea will brief the North Atlantic Council about North Korea's troop deployment to Russia on Monday, NATO said on Sunday, after the U.S. expressed grave concern over the possible use of the troops against Ukraine, Paralel.Az reports.

"Ambassadors from NATO's Indo-Pacific partners – including Australia, Japan, New Zealand and the Republic of Korea – have been invited to attend," the military alliance added. The North Atlantic Council is NATO's main decision-making body.

Ukrainian military intelligence said on Thursday that about 12,000 North Korean troops, including 500 officers and three generals, were already in Russia, and training was taking place on five military bases.

Speaking on the same day, Russian President Vladimir Putin did not deny that North Korean troops were in Russia. But he said it was Moscow's business how to implement a treaty with Pyongyang that includes a mutual defence clause to aid each other against external aggression.