Seoul, Jan 5 (IANS): A North Korean drone was found to have briefly entered a 3.7-km radius no-fly zone around the office of President Yoon Suk Yeol in Seoul in December 2022, a military official belatedly confirmed to a news agency on Thursday, reversing the defence authorities' announcement that there was no such grave airspace security failure.

The drone was among the five unmanned aerial vehicles that the North sent across the Military Demarcation Line separating the two Koreas on December 26. The South Korean military failed to shoot them down, raising questions over its air defence posture, Yonhap news agency reported.

"It briefly flew into the northern edge of the zone, but it did not come close to key security facilities," the official told the news agency on condition of anonymity, referring to the security area called "P-73".

Defence Minister Lee Jong-sup reported the drone's entry into a part of the zone to Yoon during Wednesday's briefing on counter-drone measures, such as plans to secure radar-evading drones and "drone-killer" systems.

Earlier, the Joint Chiefs of Staff rejected media reports raising speculation that the drone penetrated the zone. Its spokesperson, Col. Lee Sung-jun, even expressed "strong regrets," dismissing the reports as "untrue and groundless."

Drone incursions have laid bare the South's insufficient readiness to detect, track and shoot down such small drones. The North's drones, in particular, flew on aberrant trajectories, changing flight speed and altitudes in unexpected ways, according to the defense ministry.