A file photo of South Korea's naval ship in a drill in 2012. [Photo/IC]

The Democratic People's Republic of Korea (DPRK) on Thursday fired several rounds of artillery shells toward waters in the Republic of Korea (ROK), and two rounds fell near a ROK 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 ROK 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 ROK.

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

The shells also fell in waters some 14 km southwest of Yeonpyeong Island and south of the NLL. Residents living in the border island have been evacuated and fishing boats near the area returned to the port.

The Yeonpyeong Island is a hotspot on the Korean Peninsula as maritime skirmishes happened near the island. In November 2010, the DPRK fired artillery shells at Yeonpyong, killing two civilians and two marines.

In late March, the DPRK shot some 500 hundred rounds of shells with its artillery guns just north of the NLL, and some 100 of them fell in waters near the disputed border island. The ROK military fired back some 300 rounds.

Tensions are running high on the Korean Peninsula as the DPRK warned of a new form of nuclear test. Pyongyang launched some 90 short-range missiles in late February and March, and also fired medium-range Rodong missiles, causing a harsh denunciation from the international community.

The ROK military repeatedly said that increased activity in the DPRK's main nuclear test site was detected, and the ROK defense chief said in early May that the North has prepared for the fourth nuclear test and the preparations have been in the final stages.

The DPRK has recently conducted engine tests for an intercontinental ballistic missile known as KN-08, which was flaunted by the North during the past military parades, according to local media reports.

Some thawing signs in the inter-Korean relations were also found recently. ROK's Catholic cardinal visited the Kaesong industrial complex, and the two Koreas exchanged condolences over their respective accidents.

Cardinal Andrew Yeom Soo-jung of ROK visited the inter- Korean factory park in the DPRK's border town of Kaesong on Wednesday after Pyongyang gave a green light to it two days earlier. Yeom became the first ROK Catholic leader to visit the North.

The DPRK's rare approval to the ROK religious leader' s trip was seen by some as a conciliatory gesture.

On Tuesday, ROK delivered condolences to the DPRK over the recent collapse of an apartment building in Pyongyang.

The DPRK sent its consolation last month to ROK, which has been swept by deep sorrow across the entire nation following one of the country's deadliest maritime disasters that left more than 300 people dead or missing.

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