SEOUL, North Korean leader Kim Jong-un has called for using force against South Korean vessels violating its waters, state media said Thursday, amid concern the North could undertake provocations in the coming months. The North has long accused the South of violating its waters because the country does not recognize the current de facto sea border, known as the Northern Limit Line (NLL), and claims a self-drawn boundary south of the NLL. Kim's order, issued when he attended a test-fire of a new surface-to-sea missile on Wednesday, means that the North could use force against South Korean vessels operating north of the Pyongyang-claimed boundary even if where they are is south of the NLL. During the test-firing session, Kim accused the South of letting "various kinds of battleships intrude into the waters of the DPRK to seriously encroach upon its sovereignty," claiming that the NLL is a "ghost" line without any legal ground or justification. DPRK stands for the Democratic People's Republic of Korea, the N orth's official name. "He stressed the need for the DPRK to thoroughly defend the maritime sovereignty by force of arms and actions, not by any rhetoric, statement and public notice," the Korean Central News Agency (KCNA) said. "He gave important instructions to bolster up military preparedness particularly in the border waters north of Yonphyong Island and Paekryong Island frequently invaded by the enemies' warships including destroyers, escort ships and speedboats," the KCNA said. The two South Korean islands are just south of the NLL. Kim's order came as the North has ratcheted up tensions on the divided peninsula by branding the South as a "primary foe" and an "invariable principal enemy" and vowed to completely occupy the South in the event of war. Experts have raised concern that the North could undertake localized provocations around the sea and land borders ahead of South Korea's parliamentary elections in April or the U.S. presidential election in November. "What is clear is that when the enemy intrudes into the maritime border recognized by us, we will regard it as an encroachment upon the sovereignty of the DPRK and an armed provocation against it," the KCNA quoted Kim as saying. North Korea has long demanded the NLL be moved farther south as it was unilaterally drawn by the U.S.-led U.N. Command after the 1950-53 Korean War. Instead of the NLL, North Korea has so far insisted on its own version of the maritime demarcation lines that are drawn farther south than the NLL, such as the West Sea Security Demarcation Line and the West Sea Guard Line. It remains uncertain whether the "maritime border" that Kim referred to means such demarcation lines. It marked the first time that North Korea has mentioned the "maritime border" in its state media reports, according to Seoul's unification ministry. In a key parliamentary meeting in January, the North's leader called for revising the country's constitution to define South Korea as its "invariable principal enemy." He also called for clearly stipulati ng the political and geographic definition of North Korea's land, waters and airspace in the constitution. "As the southern border of our country has been clearly drawn, the illegal NLL and any other boundary can never be tolerated, and if the Republic of Korea violates even 0.001 millimeters of our territorial land, air and waters, it will be considered a war provocation," Kim said at the meeting. Depending on the scope of the North's "maritime border," there is a high possibility that accidental clashes could take place between South and North Korea along the tense western sea border. Waters near the NLL have been a flashpoint between the two Koreas, where three bloody naval skirmishes took place in 1999, 2002 and 2009. In March 2010, Pyongyang torpedoed a South Korean warship in the Yellow Sea, killing 46 sailors. Source: Yonhap News Agency