BRUSSELS (AP) — NATO on Monday confirmed that North Korean troops have been sent to Russia to aid in its war against Ukraine and that some have already been deployed in Russia’s Kursk region, where Russia is fighting a Ukrainian incursion.

“Today, I can confirm that North Korean troops have been sent to Russia, and that North Korean military units have been deployed to the Kursk region,” NATO Secretary-General Mark Rutte told reporters.

Rutte said that the move represents “a significant escalation” in North Korea’s involvement in the conflict and marks “a dangerous expansion of Russia’s war.”

His remarks came after a high-level South Korean delegation including top intelligence and military officials as well as senior diplomats briefed the alliance’s 32 national ambassadors at NATO headquarters in Brussels.