North Korea’s military threatened to launch “unannounced targeted strikes” against South Korea’s navy on Friday, accusing the latter of violating territorial waters off the western sea border. In “an emergency special warning,” North Korea’s military said that the South Korean navy speedboats made a “military provocation” by encroaching into the North's territorial waters in the Yellow Sea.

According to the warning, the South Korean Navy boats crossed the border two to three times a day between May 1 and May 7, South Korea’s Yonhap news agency reported.

“From this moment, it will make a sighting strike without any prior warning at any warship of the South Korean Navy intruding into the extension of demarcation line in the hotspot (of the sea),” a statement carried by the Korean Central News Agency (KCNA) said, adding that North Korea also threatened to launch stronger attacks on South Korean ships if Seoul retaliates.

Pyongyang’s warning comes amid the ongoing annual crab fishing season, which will continue until June in the waters off the Korean peninsula’s west coast. Naval forces of the two countries clashed in the region during this period in 1999 and 2002, killing many sailors from both sides, Reuters reported.

Meanwhile, an official in South Korea's Office of the Joint Chiefs of Staff criticized the warning as “insane,” and said that South Korean naval ships have not crossed the border since the end of the 1950-53 Korean War, according to Reuters.

After the Korean War ended in a ceasefire, the U.S.-led United Nations Command drew a maritime border off the west coast, known as the Northern Limit Line (NLL). However, Pyongyang has repeatedly rejected the border as illegal.

“It is not our side but your side that brings up tension along the NLL,” a spokesman for South Korea’s defense ministry, said in response to the North’s warning. “If you act provocatively while ignoring our warnings, we will sternly and strongly respond to them to the degree where you will bitterly repent.”