The Northern Limit Line is a demarcation line on the West Sea between South and North Korean waters which was established in August 1953, by the U.N. Army Commander as the U.N. and North Korea failed to produce an agreement on a maritime border, due to differences (U.N. claimed 3 nautical mile while North Korea claimed 12 nautical miles) in the armistice negotiations.
Though officially Pyongyang ignored the NLL, declaring "12-nautical mile territorial waters" in March 1955, and then establishing "50-nautical mile military zone," it tacitly recognized the NLL.
But when Pyongyang needed to raise tension, the North Korea army violated the NLL deliberately. Especially, after declaring its disapproval of the DMZ in April 1996, their intrusion over the NLL took place more frequently.
Recently North Korean navy vessels have broken into the NLL in persuit of on North Korean and Chinese boats fishing south of the NLL.
The South Korean government has taken immediate and appropriate action against Pyongyang's violation of the NLL.
Now, a couple of South Korean dissident voices are expressing concern over the possibility of scrapping the NLL, as set out here:
Amid the government’s move to put the adjustment of the Northern Limit Line (NLL) on agenda at the second inter-Korea summit slated for early October, two former reserve officers who held an important position in the department handling intelligence on North Korea for the Roh Moo-hyun and Kim Dae-jung administration said, “The NLL is a maritime trip wire.”BBC map of NLL from here.
North Korea has been tenacious in demanding the scraping of the NLL. The tension over the NLL issue is escalating in South Korea after Unification Minister Lee Jae-jung remarked in the National Assembly on August 10, “The NLL is not a territorial matter but a security matter.”
Key officials of the Unification Ministry came out supporting Minister Lee’s statement on the government’s internet newspaper site on August 22, but Cheong Wa Dae refuses to clarify its position on raising the NLL issue at the summit while just maintaining that the NLL is a virtual maritime border.
In an interview with Dong-A Ilbo yesterday, reserve officials Park Seung-chun (60) and Han Chul-yong (60), criticized the government’s ambiguous attitude, saying, “North Korea is seeking to break up the South’s security crossbar by incapacitating the NLL.”
The two said, “The NLL has preserved the peace and has been a maritime trip wire that prevented conflicts between the two Koreas for more than a half-century,” and warned that yielding the NLL would translate into removing a security shield for the Incheon and metropolitan area.
The two added, “The real intention behind the North’s move to abolish the NLL is to neutralize the South’s navy forces around the West Sea that would obstruct its attack against the South in case of a war,” and pointed out, “The claim that yielding the NLL will bring peace on the West Sea is just a fantasy that ignores the North’s military strategy against the South.