North Korea twice test fired three artillery shells into waters near a disputed maritime border with the South on Wednesday, provoking a volley of warning shorts in return. The incident heightens tension on the peninsula just after the two Koreas were on the verge of resuming negotiations.

South Korean military officials believed the North was conducting drills off its west coast but some of their shells had landed close to the maritime border, compelling Seoul to respond with a denunciation and warning shots of its own.

The South’s posturing came after its government was criticized last year when it failed to react in kind to the North Korean shelling of one of its islands, Yeonpyeong, in the same area. Four people were killed in that attack, including two civilians — a first since the end of hostilities in 1953.

The two Koreas remain technically at war. Border skirmishes, which have become frequent in recent years as the communist regime in Pyongyang struggles to survive, risk plunging Northeast Asia once again into war.

In March of last year, a South Korean warship was torpedoed and sunk, presumably by the North although it denied involvement. Forty-six sailors were killed.

North Korea’s nuclear ambitions continue to worry South Korea and its allies in the West. The regime last year announced to the world that it was nearing the final stages of uranium enrichment and had been testing intercontinental ballistic missiles.

Last month, the two Koreas and the United States discussed ways to resume talks about disarming Pyongyang’s nuclear program in return for ending its economic and political isolation. The secluded dictatorship can count only China among its friends but as the Kim dynasty will likely continue to invent crises in order to legitimize its very existence, Beijing could run out of excuses to shield its communist ally from repercussions.

There is mounting discord within the Chinese leadership over how to cope with North Korean aggression. Whereas military officials and Communist Party hardliners are prone to sympathize with the regime, civilian leaders have expressed growing puzzlement and anger about Pyongyang’s erratic behavior.