(ATTN: UPDATES with official's remarks, more details in paras 6-7, 10)
SEOUL, Jan. 5 (Yonhap) -- A North Korean drone briefly entered a 3.7-kilometer-radius no-fly zone around the office of President Yoon Suk Yeol in Seoul last month, a military official belatedly confirmed Thursday, reversing the defense authorities' announcement that there was no such incident.
The drone was among the five unmanned aerial vehicles that the North sent across the Military Demarcation Line separating the two Koreas on Dec. 26. The South Korean military failed to shoot them down, raising questions over its air defense posture.
"It briefly flew into the northern edge of the zone, but it did not come close to key security facilities," the official told Yonhap News Agency on condition of anonymity, referring to the security area called "P-73."
In a background briefing for reporters later in the day, another military official also said an object, presumed to be an enemy drone, appears to have flown through a part of the "northern tip" of the P-73 zone.
"But I would like to clarify that there was no problem regarding the security of the presidential office in Yongsan," the official stressed.
The official brushed aside speculation that the drone in question might have taken photos of the presidential office and other nearby security facilities, like the Joint Chiefs of Staff (JCS) headquarters.
"Given the distance, altitude and the enemy's capabilities, we believe it was not able to take photos at that time," he said.
Defense 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 JCS rejected media reports raising speculation that the drone penetrated the zone. Its spokesperson, Col. Lee Sung-jun, even expressed "strong regrets" in a statement, dismissing the reports as "untrue and groundless."
The shift in its formal position on the sensitive matter came apparently as relevant authorities gained more information during an ongoing JCS inspection over the botched operation against the North's drones.
Meanwhile, the military plans to conduct more air defense drills, including live-fire ones, under a scenario of small enemy drone infiltrations, Thursday afternoon, according to officials.
The drills are to involve some 50 aircraft, including KA-1 light attack planes and 500MD choppers with troops armed with drone jammer guns. The military previously staged counter-drone drills without a live-fire segment on Dec. 29, days after the North's drone infiltrations.
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.