Seoul: North Korea twice fired shells near the flashpoint Yellow Sea border with South Korea, prompting warning shots from the South's marines in response, Seoul's military said.

The incident fuelled already high tensions along the disputed sea border, which saw bloody naval skirmishes in recent years and a deadly shelling attack on South Korea's Yeonpyeong Island last November.

 The North denied shelling, with its state news agency saying on Thursday that Seoul was "faking up" the latest incident after "normal blasting" took place as part of construction work, but linking the events with joint US-South Korean military drills set for this month.

Seoul's defence ministry said a North Korean shell landed near the border -- known as the Northern Limit Line (NLL) -- at 1:00 pm (0400 GMT).

Marines based on Yeonpyeong island broadcast a warning and then fired three warning shots from K-9 self-propelled guns.

The North's coastal artillery fired again at 7:46 pm towards the border and the South again fired warning shots in response, said a ministry spokesman.

"North Korea fired two shots and one shell landed near the NLL. Our side fired three shots from the K-9," he said. "There were no more shots afterwards but we're now closely watching the situation."

The ministry said the initial shells may have been fired during a training exercise.

Citing the North's envoy to working-level military talks with the South, Pyongyang's official Korean Central News Agency (KCNA) said in a report issued early today that Seoul had fabricated the incident.