BRUSSELS (Reuters) -- NATO Secretary General Mark Rutte confirmed on Monday that North Korean troops have been sent to Russia and that North Korean military units have been deployed to the Kursk region.

"The deepening military cooperation between Russia and North Korea is a threat to both Indo-Pacific and Euro-Atlantic security," Rutte told reporters after NATO officials and diplomats received a briefing from a South Korean delegation.

Ukrainian forces staged a major incursion into Kursk in August and remain in the region.

Rutte said the North Korean deployment represented "a significant escalation" of Pyongyang's involvement in "Russia’s illegal war" in Ukraine, a breach of UN Security Council resolutions and a "dangerous expansion" of the war.

Rutte said the deployment of North Korean troops was a sign of "growing desperation" on the part of Russian President Vladimir Putin.

"Over 600,000 Russian soldiers have been killed or wounded in Putin’s war and he is unable to sustain his assault on Ukraine without foreign support," Rutte said.

The Kremlin had dismissed reports about a North Korean troop deployment as "fake news." But Putin on Thursday did not deny that North Korean troops were currently in Russia and said that it was Moscow's business how to implement a partnership treaty with Pyongyang.

A North Korean representative to the United Nations in New York called the reports "groundless rumors."