North Korean troops have not been seen on the frontlines in Russia’s Kursk region for several weeks, a Ukrainian military official said Friday, amid reports of mass casualties among Pyongyang’s forces.

The soldiers appear to have been pulled back from the front lines in Kursk after suffering heavy casualties during barely a month of combat, Ukrainian officials said.

In its first direct criticism of the Trump administration, North Korea lashed out at U.S. Secretary of State Marco Rubio for calling it a “rogue” state and warned Monday that such “coarse and nonsensical remarks” will never contribute to U.