NATO countries have confirmed evidence that North Korea has sent troops to Russia, an alliance spokeswoman said Wednesday, warning it would be a major escalation if they head to Ukraine.

"Allies have confirmed evidence of a DPRK troop deployment to Russia. If these troops are destined to fight in Ukraine, it would mark a significant escalation in North Korea's support for Russia's illegal war and yet another sign of Russia's significant losses on the front lines," Farah Dakhlallah said in a statement.

DPRK stands for the North's official name, the Democratic People's Republic of Korea. (AFP)