SEOUL (AFP/Reuters) - Two South Korean soldiers were seriously injured on Tuesday in an apparent landmine explosion while on patrol along the heavily fortified border with North Korea, a Defence Ministry spokesman said.

The two staff sergeants were on routine patrol duty in the demilitarized zone (DMZ) - a buffer zone stretching for 2km on either side of the actual frontier line dividing the two Koreas.

The soldiers, described as officers, were patrolling an area of the border in the northern county of Yeoncheon early Tuesday when the incident occurred.

"The two soldiers, with their legs shattered from the suspected landmine explosion, are now being transported to a military hospital," the spokesman told AFP.

One military official, who asked not to be identified, said the incident possibly involved a landmine and was being investigated.

The blast happened near the town of Paju, close to the border with North Korea, about 50km north of Seoul.

Military officials said both men had been wounded in the legs but their wounds were not life-threatening.

Defence Ministry spokesman Kim Min Seok expressed his sorrow over the incident.

Despite its name, the DMZ is a heavily militarised area, and peppered with minefields on both sides.

There are telephones on the South Korean side for defectors from the impoverished and reclusive North to call seeking help, although it was not immediately clear if Tuesday's incident involved North Korea.

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.

When the United States - the South's key military ally - declared last year that it was halting the use of all anti-personnel mines, it made an exception for the inter-Korean border, citing the area's "unique challenges".