North and South Korea fired warning shots at each other’s ships early Monday and accused each other of unwarranted incursions of the maritime demarcation line in the Yellow Sea, according to statements released by each side’s militaries. 

A North Korean merchant ship named the Mupho-ho started the latest spat by “intruding” over the Northern Limit Line (NLL) around 16 miles (27 km) northwest of South Korea’s Baengnyeong Island at 3:42 a.m. KST, Seoul’s Joint Chiefs of Staff (JCS) said in a statement.

The South Korean military sounded warnings and fired warning shots in an unspecified place in response, JCS said,