South and North Korea breached the armistice agreement by flying drones across the inter-Korean border last December, said the United Nations Command on Thursday.

South Korea disputed the UNC’s conclusion, saying that sending drones to North Korea after Pyongyang’s infiltration was carried out in “self-defense,” which is not restricted by the armistice agreement.

The special investigation team was able to determine that the North Korean military “committed a violation of the Armistice when multiple North-side unmanned aerial systems (UAS) entered ROK-controlled airspace,” the UNC said in a statement, referring to South Korea by the acronym of its official name, Republic of Korea.

Five North Korean unmanned aerial vehicles, or UAVs, infiltrated South Korea and flew over Seoul and residential areas along the western border for several hours. One of them violated a no-fly zone designated for the purpose of presidential security.

The South Korean military scrambled Air Force fighter jets and attack helicopters and fired around 100 shots from an attack helicopter toward a North Korean drone near Ganghwado, Incheon. But it failed to bring down any of the North Korean UAVs.

The UNC concluded that the South Korean military’s attempts to neutralize North Korean UAVs in South Korean airspace was in “compliance with the Armistice Rules of Engagement and consistent with the Armistice.”

But the UNC did not recognize the legitimacy of the South Korean military’s retaliation. The military flew its reconnaissance UAVs north of the military demarcation line separating the two Koreas.

The special investigation team was able to “determine that the employment of ROK military UAS across the Demilitarized Zone and into DPRK-controlled airspace constitutes a violation of the Armistice,” the UNC said in the statement, referring to North Korea by the acronym of its official name, Democratic People’s Republic of Korea.

The UNC is not obliged to publicly announce the results of its investigation on the compliance of the armistice agreement.

The UNC, therefore, had been internally reviewing whether to publicize the outcome of the investigation as the command has concerns that its pronouncement might be misused by political powers in South Korea, The Korea Herald learned. The main opposition Democratic Party of Korea first made a claim that the South Korean military violated the armistice agreement.

South Korea’s Defense Ministry on Thursday said its “tit-for-tat action is not restricted by armistice agreement given that it intended to protect its right of self-defense” laid down in Article 51 of the UN Charter.

Article 51 stipulates that the charter does not proscribe the “inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations.”

The ministry said it viewed that the UNC has reached the conclusion in light of its mission to enforce the 1953 Korean Armistice Agreement that brought about a cessation of the Korean War.

The UNC has taken a case-by-case evaluation of whether the South Korean military’s countermeasures against previous North Korea’s cross-border offensives violated the Korean Armistice Agreement was legitimate.

In a previous case, the UNC acknowledged the legitimacy of the firing back by South Korea’s Marine Corps in response to the North Korean bombardment of Yeonpyeong Island in November 2010. At that time, the UNC said the South Korean military action was an exercise of the right of self-defense and did not breach the Korean Armistice Agreement and the UN Charter.

In contrast, the UNC concluded that the South Korean military violated the armistice agreement in May 2020 by returning fire after North Korea fired small arms directed at a guard post located south of the military demarcation line.