North Korean state media reported this week that leader Kim Jong Un observed live-fire military drills, which included paratrooper exercises and an air force display. South Korea's Yonhap news agency reports that authorities in Seoul say there are around 200,000 members of an elite North Korean force trained in special operations.
A source familiar with the North Korean military told Yonhap on condition of anonymity that recent drills were more active than usual.
"Overall, its winter training has increased aggression," the source said.
North Korea conducted its third underground nuclear test in mid-February. Beijing has been pressed to use its influence with Pyongyang to help allay international concerns, though Chinese officials this week said its position was overstated.
North Korea hinted it would respond to restrictive action from the U.N. Security Council with more rocket or nuclear tests. The Security Council had an emergency session regarding North Korea's latest nuclear test.
Patrick Ventrell, a spokesman for the U.S. State Department, said Pyongyang was better served to "focus their money on feeding their children" than on its military.