South Korea said planned military firing drills would go ahead on Monday near a disputed maritime border with North Korea, which has threatened "merciless retaliation" if Seoul fires into its waters on the anniversary of a 2010 bombing that killed four people.

Five years ago North Korea fired artillery at the South's Yeonpyeong island, which lies south of the Northern Limit Line (NLL) sea border off their west coast, in what was the first attack on South Korean soil by the North since the 1950-53 Korean War.

North Korea has said it was provoked into the attack by South Korean live-fire drills in the area that dropped shells in its territorial waters.

South Korea's Defense Ministry spokesman Kim Min-seok said on Monday there was no sign of unusual activities by the North Korean forces.

"The firing drills are regularly scheduled drills, and if the North mounts a provocation, we will respond strongly under our operational plan," Kim told a briefing.

North Korea's military said on Sunday the South "will experience merciless retaliation of the Southwestern Front units of the DPRK on the five islands," if Seoul's firing drills crossed into its waters.

DPRK is the acronym for the North's formal name, the Democratic People's Republic of Korea. Five islands including Yeonpyeong lie close to the disputed border.

On Friday, the rival Koreas agreed to hold talks on Nov. 26 in what would be the first government-level meetings focused on easing tensions since the two pledged to improve ties following an armed standoff in August.