A navy patrol boat of the Democratic People's Republic of Korea (DPRK) briefly crossed the western inter-Korean sea border on Saturday, said the office of the Joint Chiefs of Staff (JCS) of South Korea.

The vessel crossed the controversial Northern Limit Line (NLL),about 8 miles off Yonpyeong Island of South Korea at 0:48 a.m. (1548 GMT) Saturday but returned to the DPRK side 10 minutes later as a South Korean speedboat approached, the JCS said.

The incident occurred while the DPRK boat was trying to crack down on about 20 other country's fishing boats poaching in the area, added the JCS.

The South Korean navy sent two warning radio messages via a shared radio frequency, but the DPRK boat did not respond, according to the JCS.

"Considering the DPRK's vessel was a small-sized patrol boat, it might have not been properly equipped to receive radio messages from South Korea. A further analysis on this is necessary," the office said.

In June, Seoul and Pyongyang agreed to have their navies share a radio frequency and use the same flag signaling system to avoid accidental clashes on the poorly marked maritime border.

The DPRK has not completely accepted the NLL as sea boundary with South Korea, while Seoul holds the NLL is the de-facto inter-Korean sea border on the Yellow Sea.

The two sides had two naval skirmishes in 1999 and 2000 around the NLL, which resulted in heavy casualties on both sides.

Source: Xinhua