North Korea fired ten artillery shells toward a buffer zone in the Yellow Sea on Monday after the South Korean military repelled a North Korean commercial vessel violating the de facto maritime border earlier in the day.

The Joint Chiefs of Staff(JCS) said it detected the artillery shots launched from around Jangsan Cape, South Hwanghae Province from 5:14 a.m. into the buffer zone north of the Northern Limit Line(NLL), none of which landed in South Korean territory.

The JCS said the North’s artillery shell firing in response to South Korea’s actions against a North Korean vessel that crossed the NLL is a clear violation of the inter-Korean military agreement and a provocation.

Continuous provocations by the North and its absurd claims harm the peace and stability of the Korean Peninsula and international community, the JCS said, urging Pyongyang to stop such activities.

The JCS said the military is monitoring related activities in coordination with the U.S. and strengthening readiness against a possible contingency.

Earlier in the day, a North Korean merchant ship crossed the NLL, the de facto maritime border between the two Koreas, before retreating after the South Korean military fired warning shots.