U.S. State Department Spokesperson Matthew Miller warned that if North Korean troops crossed the border into Ukraine to fight for Russia, that would mark a serious "escalation" in the war.

At least 30 North Koreans were “killed or wounded” over the weekend while fighting for Russia in the Kursk region, Ukrainian military intelligence said.

In an interview with CBS News on Dec. 15, Ukraine's ambassador to the U.S. Oksana Markarova said that "hundreds" of North Korean troops are fighting alongside Russian troops in Kursk Oblast. "We have seen hundreds of (North Korean soliders) on the battlefield already,