North Korea has denied shelling near South Korea's border and accuses Seoul of war mongering.
The state-run Korea Central News Agency carried a report Wednesday denying any firing in the waters near the South Korean island of Yeonpyeong in the Yellow Sea.
Earlier in the day, South Korean news media said the two sides had exchanged artillery fire Wednesday near the maritime border between the two Koreas. Reports quoted a defense ministry official in Seoul as saying all shells fell into the sea and there were no reports of damage or injuries on the island.
Yonhap news agency quoted officials as saying a second short North Korean volley was heard on Yeonpyeong later Wednesday, but it was not clear whether the island was targeted.
But the report from Pyongyang responded that North Korea is constructing what it called a gigantic object in its southern Hwanghae province close to five islands in the West Sea and that August 10 blasting was part of the construction work.
North Korea shelled the South's Yeonpyeong island in November killing four people.
The attack severely damaged relations between the two Koreas, which were already strained by the sinking of a South Korean warship in March 2010.
Tensions between the two Koreas have eased somewhat this year after the two sides came close to an armed conflict last year. In recent weeks parties in the six-nation talks on North Korea's nuclear disarmament have made diplomatic efforts aimed at a resumption of the aid-for-disarmament talks. The last round of those talks was held in China in 2008.
In the first significant sign of a thaw, senior diplomats held what they described as constructive talks last month on the sidelines of a regional security conference in Bali, Indonesia.
A North Korean delegation later visited New York for additional talks with U.S. officials.