NATO Secretary General Mark Rutte addresses the media during a press conference with Finland's President at the NATO headquarters in Brussels, on October 8. (AFP)

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)