DPRK?soldiers are seen on a boat on the banks of the Yalu River on?October 6, 2014.[Photo/Agencies]

SEOUL -- Naval ships of the two Koreas traded warning fires in the western sea boundary after a patrol ship of the Democratic People's Republic of Korea (DPRK) violated the disputed maritime border, Yonhap News Agency and YTN reported Tuesday.

One DPRK patrol ship sailed around 1 km south of the Northern Limit Line (NLL) at about 9:50 a.m., violating the disputed western sea border, South Korea's Joint Chiefs of Staff (JCS) was quoted as saying.

A South Korean high-speed boat, or called PGM (guided missile patrol gun boat), issued warning communications to make the DPRK ship return to its territorial waters, but the DPRK ship stayed there until the South Korean ship issued warning fires with machine gun.

The DPRK ship fired back at the South Korean ship, which in response fired machine guns against the DPRK ship.

After exchanging machine gun shots, the DPRK patrol ship returned to the north.

No warships of both sides fired aimed shots against each other. No casualties have been reported from the South Korean ships.

The JCS said the South Korean military strengthened its monitoring of DPRK forces, fully preparing for possible emergency situations.

On Sept 19, one fishery inspection boat of the DPRK violated the NLL and returned back to the north after South Korea's warning shots.

On May 22, DPRK naval ships fired several rounds of artillery shells toward waters near the NLL and two rounds fell near a South Korean patrol ship sailing in the waters.