SEOUL, May 22 -- The Democratic People's Republic of Korea (DPRK) on Thursday fired several rounds of artillery shells toward waters in South Korea, and two rounds fell near a South Korean patrol ship sailing around the western maritime border.

"Two shells landed near our boat patrolling in our territorial waters near the Northern Limit Line (NLL) at around 6 p.m. (local time)," a South Korean defense ministry official told Xinhua on condition of anonymity. "Our boat fired back several rounds of shells in response to it."

No injuries and damages from the South Korean patrol ship have been reported, the official said, noting that the military is closely monitoring and preparing for possibly further provocations.

Military officials were quoted by local media as saying that the shells fell just about 150 meters away from the battleship, indicating the DPRK took a direct aim at the ship on a patrol mission. Whether it was an aimed shot or a warning shot had yet to be confirmed by the military.

Given the preciseness, the rounds were believed to be fired from artillery positions in the DPRK's southwestern coast bordering South Korea.

The firing came a day after the Southwestern Command of the Korean People's Army warned of an "aimed shot" at South Korean battleships.

The DPRK issued the warning as South Korea fired several warning shots at the DPRK patrol ships, which violated the inter- Korean sea border on Tuesday.