Several North Korean soldiers working near the heavily fortified border with the South were wounded in a landmine explosion, the Yonhap News Agency said Tuesday, citing Seoul's Joint Chiefs of Staff.

"North Korean military suffered multiple casualties due to a mine explosion during work," it said, without giving further details. The border between the two countries is heavily mined.

South Korea's military said the explosions came after dozens of North Korean soldiers briefly crossed the border but retreated after Seoul's military fired warning shots.

It was the second such incursion in two weeks. (AFP)