South Korea's military said Monday it was "fully ready" to respond after North Korea ordered troops on the border to prepare to fire, in an escalating dispute over drone flights to Pyongyang.

The nuclear-armed North has accused Seoul of flying drones over its capital to drop propaganda leaflets filled with "inflammatory rumors and rubbish," and warned Sunday that if another drone was detected, it would consider it "a declaration of war."

Seoul's military previously denied it was behind the flights, with local speculation centered on activist groups in the South, which have long sent propaganda and U.S. currency northward, typically by balloon.