A North Korean drone entered the northern end of a no-fly zone surrounding South Korea’s presidential office in Seoul when it intruded into the South’s airspace last week, the South’s military said on Thursday.

The drone was among five North Korean drones that crossed into the South on Dec. 26, prompting South Korea’s military to scramble fighter jets and attack helicopters. The military was unable to bring down the drones, which flew over the South for hours.

South Korea’s Joint Chiefs of Staff (JCS) had denied that one of the drones intruded into a no-fly zone near the presidential office, but on Thursday reversed its stance and confirmed it had violated the northern end of the area.

A JCS spokesperson said there was a change in its analysis after an inspection of the military’s readiness posture over the latest intrusion.

The military said the North’s unmanned aircraft did not fly directly over the Yongsan area, where the office of President Yoon Suk-yeol is located.

The border crossing has sparked criticism over South Korea’s air defences at a time of the North’s growing nuclear and missile threats.

Yoon has warned he would consider suspending a 2018 inter-Korean military pact if the North violates its airspace again.