Military tensions between the two Korea countries ramped up on Monday when South Korea accused North Korea of planting landmines that maimed two soldiers on border patrol, and threatened to make Pyongyang pay a "harsh price".
The defence ministry said it believed three landmines exploded in the incident last Tuesday, hitting a patrol in the demilitarized zone (DMZ) - a buffer zone stretching two kilometres on either side of the actual frontier line dividing the two Koreas.
"We are certain they were North Korean landmines planted with an intention to kill by our enemies who sneaked across the military border," ministry spokesman Kim Min-Seok told reporters. One soldier underwent a double leg amputation, while the other had one leg removed.
In a statement, the South's Joint Chiefs of Staff said its military would make North Korea "pay a harsh price proportionate for the provocation it made."
Describing the attack as a "baseless act" and "wanton violation" of non-aggression accords, the statement urged the North to apologise for the attack and punish those responsible. The Defence Ministry declined to comment on what was meant by the term "harsh price" or to speculate on the options being considered for a response.
Few options for retaliation
Analysts said the type of incident made a proportionate response difficult to gauge.
"Realistically, it's hard to see what South Korea can actually do," said Dan Pinkston, Korea expert at the International Crisis Group in Seoul.
"It's an unacceptable breach of the armistice terms, but you don't want to escalate the situation so it spins out of control. It's very difficult," Pinkston told AFP.
There was no immediate response from North Korea to the charge that its military planted the devices.
The last direct attack on the South was in November 2010 when North Korea shelled the South Korean border island of Yeonpyeong, killing two civilians and two soldiers.
South Korea responded by shelling North Korean positions, triggering brief fears of a full scale conflict.
The rival Koreas remain technically at war because their 1950-53 Korean conflict ended in a ceasefire rather than a peace treaty. The UN Command that monitors the ceasefire accord said Monday that it had conducted a special investigation into last week's blasts and concluded they were North Korean "wooden box" land mines placed on a known South Korean border patrol path.
"The investigation determined that the devices were recently emplaced, and ruled out the possibility that these were legacy landmines which had drifted from their original placements," it said in a statement.
More than a million mines are believed to have been planted along the inter-Korean border, including those which were air-dropped in great numbers in the 1960s at the height of a Cold War confrontation with the North.
Intention to kill
South Korean Brigadier General Ahn Young-Ho said 43 pieces of the exploded landmines had been recovered from the scene and analysed.
"Our troops have operated in this area on a regular basis," Ahn said.
"These mines were planted by the North Korean military with an intention to kill our soldiers," he added.
The incident comes at a sensitive time, with both Koreas preparing to commemorate the 70th anniversary on Saturday of the 1945 liberation of the Korean peninsula from Japanese rule.
There had been hopes that the anniversary might open an opportunity for some sort of rapprochement, but efforts to organise a joint commemoration went nowhere with Pyongyang refusing to consider talks because of Seoul's refusal to cancel annual joint military exercises with the United States.
Yang Moo-Jin, a professor at the University of North Korean Studies in Seoul, said North Korea was almost certain to deny planting the mines, and added that it was difficult to deduce any motive for such an operation.
"Maybe it is just a pre-meditated provocation to heighten military tensions," Yang said.
"Whatever the reason, South Korea has limited options to respond, especially inside the DMZ where military activity is so closely controlled and monitored," he added.
Despite its name, the DMZ is one of the most heavily-militarised frontiers on the planet.