North Korea on Tuesday warned that recent "provocative" activities by US troops at a truce village on the heavily fortified inter-Korean border could lead to a "catastrophic" military clash.

The warning came from the head of the North Korean forces stationed in the frontier village of Panmunjom -- where the ceasefire agreement to end fighting in the 1950-53 Korean War was signed.

Panmunjom has hosted multiple inter-Korean talks over the decades and is heavily guarded, with mostly South Korean and US troops on the southern side under the auspices of the UN Command (UNC).

The North Korean military official, who was not named, said recent activities by US troops threatened to destabilise the sensitive area.

In remarks carried by the North's official KCNA news agency, he particularly cited the construction of a steel watchtower, saying it was being used for "acts of spying" involving sophisticated surveillance equipment.

Given the military sensitivity of Panmunjom, where North and South Korean border guards stand almost eyeball-to-eyeball, the official said such activity was particularly dangerous.

"The slightest accidental mistake or undesirable behaviour could lead to a catastrophic military clash," he said.

North Korea regularly denounces the US troop presence in the South, but it is unusual for it to focus on activities in Panmunjom -- one of the few avenues of cross-border communication.

A UNC spokesman dismissed the North's concerns, saying the watchtower had been constructed for "ordinary monitoring purposes".

The North Korean official cited other "sinister" activity by US troops, including messages relayed across the border by loudspeaker and letters with "dishonest contents" that were left in huts straddling the border.

Such actions had multiplied since US President Barack Obama visited South Korea in April, he said.

During that visit, Obama called the impoverished but nuclear-armed North a weak "pariah state" that was intent on taking "a path that leads only to more isolation".

Military tensions between the two Koreas have been elevated for several months.

Last week, Seoul said a North Korean warship fired shells near one of its naval corvettes and denounced Pyongyang's denial as a "blatant lie".

Panmunjom has generally been sheltered from the volatile swings in inter-Korean relations, although it has witnessed a number of deadly incidents.

There were fears of a full-scale conflict in 1976, after a group of axe-wielding North Korean troops killed two American soldiers who were trimming a tree on the border.