North Korea warned Sunday of "merciless" attacks on South Korean border islands if Seoul stages live-fire drills near the maritime border on the fifth anniversary of Pyongyang's deadly shelling attack.

The bombardment of Yeonpyeong island off the west coast on November 23, 2010 killed four South Koreans including two civilians and sparked brief fears of full-scale war.

South Korea's military has in the past staged live-fire exercises near the Yellow Sea border around the anniversary as a show of strength.

The North's Southwestern Front Command in charge of the tense border area accused Seoul Sunday of planning another "provocative" live-fire drill to mark the fifth anniversary.

"If the South Korean military fires at the waters of the (North)...on Monday, they will experience merciless retaliation of the Southwestern Front units...on the five (border) islands," it said in a statement carried by the state-run Korean Central News Agency.

It was not known whether the South would stage any such exercise and the defence ministry was not available for comment.

Pyongyang, known for its habitual warnings of attacks on the South, rarely follows through with such threats.

"The bellicose forces of the South Korean military should come to their senses," Sunday's statement said.

It urged Seoul to honour a recent agreement aimed at easing tension sparked by a landmine explosion that maimed two South Korean border guards and was blamed on Pyongyang.

The agreement also paved the way for a rare reunion of families separated by the 1950-53 Korean War. This was held last month amid signs of a thaw in icy ties.

The Yellow Sea border -- unilaterally drawn by US-led UN forces at the end of the war and not recognised by Pyongyang -- was the scene of deadly naval clashes in 1999, 2002 and 2009.