The UN Command has determined that North Korea violated the 1953 Korean War Armistice by sending drones into South Korea's airspace in December last year.

Five North Korean drones entered South Korean airspace on December 26 across the military demarcation line. One of them reached north of the capital Seoul before flying back home.

The UN Command released on Thursday the outcome of a probe conducted by a special investigation team into the drone infiltrations. It reported the armistice violation by North Korea.

In the incident, South Korean helicopters and other aircraft fired on the drones in the South's airspace.

The UN team says the South Korean action is in compliance with the Armistice Rules of Engagement, and consistent with the armistice.

But the team also found a violation by the South at that time. The South Korean military sent reconnaissance drones into the North's airspace to take photos of military facilities below there. The UN team determined the South Korean conduct constitutes an armistice breach.

South Korea's defense ministry has defended the deployment of drones as an exercise of its right to self-defense. It says the right is not restricted by the armistice.

South Korea's military has come under criticism at home after it came to light that it took action on the North Korean drones more than an hour after finding them.

South Korea's Joint Chiefs of Staff apologized over the incident during a parliamentary committee meeting on Thursday. Opposition lawmakers demanded that military leaders should take the blame and responsibility for the operational failure.