The recently signed mutual defense treaty could be used to justify thewidening of the war in Ukraine, as the U.S. says North Korean and Russian troops are already battling Ukrainian forces.

U.S. State Department spokesperson Vedant Patel says on November 12 that the majority of some 10,000 North Korean troops sent to support Russia’s war against Ukraine are now “engaging in combat operations” in Russia’s western Kursk region.

Russia’s military is employing World War One-style tactics, involving relentless human wave attacks and heavy artillery, to make incremental gains in eastern Ukraine, notably around urban centers like Vuhledar.