South Korea is claiming North Korean artillery drills have invalidated long-established buffer zones.

The South Korean Joint Chiefs of Staff announced Monday that it will resume drills in the area in response to the North Korean artillery bombardment, saying the restrictions on the zone “no longer exist.”

An agreement in 2018 between Seoul and Pyongyang established the buffer zones as a prohibited area for artillery fire or military drills.

Earlier this month, the North Korean military initiated a multiday bombardment of the border region with hundreds of artillery rounds in a series of military drills.

South Korean intelligence estimates approximately 200 shells fired into the area on Friday and an additional 60 on Saturday.

The South Korean Defense Ministry reportedly fired approximately 400 rounds in response to the provocation.

“We gravely warn that the entire responsibility of such crisis-escalating situations lies with North Korea and strongly call for its immediate halt,” South Korean Joint Chiefs of Staff spokesman Col. Lee Sung-jun said at a press conference during the artillery fire.

The western sea border between North Korean and South Korean territory has been the site of multiple skirmishes since the end of the Korean War. 

Naval combat broke out briefly in 1999, 2022 and 2009.