South Korea announced Wednesday a series of heavy-weaponry, live-fire military drills with the United States as part response to a recent landmine attack blamed on North Korea.

Four exercises, involving tanks, howitzers, attack helicopters and fighter bombers, will be held in the coming weeks in an area around 30 kilometers (18 miles) south of the North Korean border, the defence ministry said.

"This will show our preparedness to retaliate against any provocative acts, including such a treacherous act of aggression as the landmine attack", a ministry spokesman said.

The first drill was to take place later Wednesday, with the last one conducted towards the end of the month.

They will be separate from the full-scale, annual "Ulchi Freedom" joint exercise that kicks off next Monday and lasts for two weeks.

The annual drills always trigger a surge in military tensions with the nuclear-armed North which has repeatedly condemned them as rehearsals for invasion.

South Korea has vowed the North will pay a "harsh price" for the mine blasts that maimed two its soldiers on border patrol last week.

The military said investigations showed North Korean soldiers had sneaked across the border to plant the mines along a known patrol route.

Pyongyang has yet to respond to the charge.

South Korea has ramped up border security in the wake of the blasts and -- after a break of more than a decade -- resumed the broadcast of propaganda messages into the North, using batteries of powerful loudspeakers set up at several sites along the border.