North Korean soldiers had been injured when a landmine exploded near the border.

Dozens of North Korean soldiers briefly crossed the heavily fortified border with the South on Tuesday and retreated after warning shots were fired, Seoul's military said, adding landmine explosions had injured Pyongyang's troops in the area.

It is the second such incident involving North Korean troops in two weeks, with Seoul's Joint Chiefs of Staff saying they believed the Tuesday crossing -- like a previous one on June 9 -- was accidental.

 

Dozens of North Korean troops crossed the Military Demarcation Line today... (and) retreated northwards after warning shots" were fired, a JCS official said. 

Seoul's military also said Tuesday that several North Korean soldiers had been injured when a landmine exploded near the border, without revealing the date.

The North Koreans were working on creating "barren land" and laying mines along the border, an official from the JCS said, but ended up "suffering multiple casualties from repeated landmine explosion incidents during their work". 

Even so, the North's military "appear to be recklessly pressing ahead with the operations," the official said.

This year, North Korea has been working to remove streetlights from roads and dig up railway tracks that connected the two countries when ties were better, they added.

Since April, North Korea has deployed troops along the front line "to create barren land", the official said, adding the North was also laying more landmines, reinforcing tactical roads, and adding what appeared to be anti-tank barriers.

"North Korea's activities seem to be a measure to strengthen internal control, such as blocking North Korean troops and North Koreans from defecting to the South," the JCS official said.

The vast majority of North Koreans who escape the country first go to China before making their way to the South, usually via another country, with only a handful ever managing to cross the DMZ, which is riddled with landmines and has a heavy military presence on both sides..