SEOUL, South Korea (AFP) — President Yoon Suk-yeol said Thursday that South Korea must boost its preparedness to respond to airspace intrusions after the military failed to shoot down five North Korean drones that crossed the border.

Yoon said Thursday that the incident was "intolerable" and added that the South should ensure that Pyongyang "realize that provocations are always met with harsh consequences."

"In order for us to achieve peace, we need to make overwhelmingly superior war preparations," he said during a visit to the state-run Agency for Defense Development.

"The overall response system against all flying objects invading our airspace, on top of drones, must be re-examined to quickly make up for deficiencies."

Yoon earlier this week slammed the military's handling of the incident, and ordered the acceleration of a plan to launch a drone unit, which would include advanced stealth models, to carry out surveillance on Pyongyang's key military facilities.

The South's Joint Chiefs of Staff also said on Thursday it would stage exercises focused on drones.

The Monday intrusion by the drones — one of which flew close to the capital Seoul — prompted the South's military to deploy fighter jets and attack helicopters.