South Korea's military on Monday threatened retaliation against North Korea after accusing the North of planting land mines inside the Demilitarised Zone border that wounded two soldiers last week, in what it called a cowardly act of provocation.

There was evidence to conclude that soldiers from the North crossed the Military Demarcation Line recently to plant the mines, and Pyongyang would be made to "pay a severe price", the South's military told a news briefing.

"We strongly condemn this cowardly act, which would be unthinkable for a normal military," Major General Ku Hong-mo of South Korea's Joint Chiefs of Staff said, calling it a violation of the armistice agreement that ended the 1950-53 Korean War.

Later on Monday, as part of its countermeasures, the South Korean military used loudspeakers to blare anti-Pyongyang rhetoric across the border, a defence ministry official said, resuming broadcasts that had been suspended since 2004.

The United Nations Command, headed by the U.S. military and which oversees the armistice, also condemned what it called the North's violation of the truce. It said it would call for a meeting with North Korea's military.

The area around last Tuesday's blast had been swept for mines and the terrain made it impossible for mines planted elsewhere to have drifted due to rain or shifting soil, South Korea's military said.

Fragments from the exploded mines also had paint typically used by the North, it said.

Two soldiers who were part of a team conducting a routine search operation inside the heavily fortified DMZ near the town of Paju, about 50 km (30 miles) north of Seoul, were seriously wounded in the blast.