SEOUL, South Korea (AFP) — South Korea fired warning shots at North Korean soldiers that briefly crossed the heavily fortified border earlier this week, Seoul said Saturday after Pyongyang accused it of risking “uncontrollable” tensions.

South Korea’s new leader Lee Jae Myung has sought warmer ties with the nuclear-armed North and vowed to build “military trust,” but Pyongyang has said it has no interest in improving relations with Seoul.

Seoul’s military said several North Korean soldiers crossed the border Tuesday while working in the heavily mined Demilitarized Zone separating the two Koreas.

The incursion prompted “our military to fire warning shots,” Seoul’s Joint Chiefs of Staff said in a statement, adding “the North Korean soldiers then moved north” of the de facto border.

Pyongyang’s state media said earlier Saturday that the incident occurred as North Korean soldiers worked to permanently seal the frontier dividing the peninsula, citing a statement by Army Lieutenant General Ko Jong Chol.

Calling the event a “premeditated and deliberate provocation,” Ko said Seoul’s military used a machine gun to fire more than 10 warning shots towards the North’s troops, according to the official Korean Central News Agency.

“This is a very serious prelude that would inevitably drive the situation in the southern border area where a huge number of forces are stationing in confrontation with each other to the uncontrollable phase,” Ko said.

The last border confrontation between the arch-rivals was in early April when South Korea’s military fired warning shots after around 10 North Korean soldiers briefly crossed the frontier.