Tensions between South and North Korea have been mounting in the last few months and according to a new report from the Associated Press "South Korean marines returned fire Wednesday after North Korea launched artillery shells into waters near the disputed maritime line that separates the two rivals."

According to the Defence Ministry spokesman Kim Min-seok North Korea was the first to open fire near the Northern Limit Line in the Yellow Sea, which was met by a retort form the South as three shells were fired back. Both sides' shells landed in the water, and there were no reports of casualties, Kim Min-seok added.

Tensions grew in November after a North Korean artillery attack killed four people on South Korea's Yeonpyeong Island, prompting South Korean forces to up their security surveillance in the area.

Wednesday's artillery exchange was located near that island, making the area a 'hot spot' of the conflict.

The Associated Press also cite another anonymous defence ministry official, who said that South Korean marines on Yeonpyeong returned fire after North Korea fired from one of its front-line islands.

While details of the exchange are still emerging, it seems that despite an atmosphere surrounded by suspicions for the last months, the North Korean move took South Korea by surprise, especially as neither side was conducting firing drills at the time and no real motive has yet been identified.

The area has been the stage of a violent confrontation as it still is a contested slice of sea and a dozen of lives have been lost since the standoff started in the 1990's.

Kim said one North Korean artillery shell is believed to have fallen south of the maritime line, citing a preliminary analysis of the trajectory of the shell.

The line separating the countries was drawn at the close of the Korean War but both countries have struggled with the frontiers delimitation ever since and the countries are technically still at war after the 1950-53 Korean War.