The Democratic People's Republic of Korea (DPRK) forces may fire on ships crossing into the area between the Northern Limit Line (NLL) and the water border it claims to the South, according to the official KCNA news agency.

The DPRK would "use armed force" to defend the demarcation line with South Korean on the west coast of the Korean peninsula, the KCNA quoted an anonymous navy spokesman as saying on Monday.

The spokesman accused South Korea of attempting to turn the NLL into its permanent water border and using military provocation in the region.

The DPRK rejected the NLL and only recognized the demarcation line it drew in 1999, which was further south of the NLL, the spokesman said. He warned that the region between the NLL and the demarcation line was within the coverage of its artillery and all ships entering that region should "take self-protecting measures."

The NLL was drawn after the 1950-1953 Korean War by the United Nations Command. South Korea holds the NLL as the de-facto western inter-Korean border, while the DPRK has not accepted it.

The North demands that the maritime border in the Yellow Sea, which was set closer to its coast should be re-drawn further south. While South Korea has rejected the North's demand to safeguard its five islands dotting the border.

The navies of the two sides have had three clashes, in 1999, 2002 and this November, around the NLL waters, which resulted in heavy casualties on both sides.