North Korea has sent at least 3,000 troops to eastern Russia this month, both Washington and Seoul confirmed, with the White House saying that any soldiers deployed on the battlefield would be "fair game.

Defense Secretary Lloyd J. Austin III called the situation “very, very serious,” though he said that what the soldiers were doing in Russia was “left to be seen.”

The U.S. says 3,000 North Korean troops have deployed to Russia and are training at several locations, calling the move very serious.