A North Korean merchant ship crossed the Northern Limit Line(NLL), the de facto maritime border between the two Koreas in the Yellow Sea, on Monday.

The Joint Chiefs of Staff(JCS) said the North Korean vessel, the Mupo, violated the NLL some 27 kilometers northwest of Baengnyeong Island in the West Sea at around 3:42 a.m.

The military sent a warning message through a communication line and also fired warning shots compelling the vessel to retreat, it said.

The military regards the crossing of the NLL as an “intrusion” and is analyzing the circumstances related to the incident.

Earlier in March, another North Korean vessel crossed the NLL along with a North Korean patrol boat in pursuit, prompting South Korean military responses.

A similar incident also occurred in November of 2019, when a North Korean ship was spotted crossing the NLL in waters off Baengnyeong Island and heading south before retreating.