SEOUL (Reuters) -North Korea said on Saturday it had discovered the remains of a crashed South Korean military drone, suggesting it was on a propaganda mission in the latest confrontation between the two involving cross-border flying objects.

"In light of the drone's shape, the presumptive period of flight, the leaflet-scattering box fixed to the underpart of the drone's fuselage, etc., it is quite likely that the drone is the one which scattered leaflets over the center of Pyongyang Municipality. But the conclusion has not yet been drawn," said state news agency KCNA.

South Korea's government has declined to say if such drones were flown and if they were, whether they were flown by its military or civilians. It said to comment on the North's claim would be to get drawn into a ploy.

"If a violation of the DPRK's territorial ground, air and waters by ROK's military means is discovered and confirmed again, it will be regarded as a grave military provocation against the sovereignty of the DPRK and a declaration of war and an immediate retaliatory attack will be launched," KCNA added.

DPRK is short for the Democratic People's Republic of Korea, North Korea's official name, and ROK stands for Republic of Korea, the South's formal name.

"North Korea's one-sided claims are not worth verifying, nor do they merit a response," South Korea's defence ministry said in a statement.

Tensions between the Koreas have escalated since the North began flying balloons carrying trash across the border to the South in late May, with Seoul responding by restarting loudspeaker propaganda broadcasts, which anger Pyongyang.

North Korea has intensified its hostile rhetoric in recent days, accusing the South's military of flying drones over its capital on three days this month and threatening "a horrible disaster" if it detects another drone over its skies.

(Reporting by Heekyong Yang and Josh Smith; Editing by Leslie Adler, Sandra Maler and William Mallard)