Soldiers from both countries face off at the JSA north of Seoul, which is overseen by the US-led United Nations Command.

North and South Korea agreed to disarm their troops on the JSA in line with a 2018 military pact, but the North's troops have been reported to carry guns since November after the deal began to crumble.

Last month, Seoul partially suspended the five-year-old accord following Pyongyang's launch of a spy satellite.

North Korea responded by scrapping the pact in full, pledging to deploy stronger armed forces and new weapons along the border.

The decision to allow the UNC troops to carry guns came after North Korean soldiers resumed "an armed security posture", the UNC said in a statement.

"The UNC has authorized trained and qualified members of the guard forces on the UNC side of the JSA to re-arm to protect both civilian and military personnel," it added.

"This action is being taken out of an abundance of caution, but UNC has also informed the ROK (South Korean) government and KPA of its position that a disarmed JSA is safer and more peaceful."

Most of the border between the two Koreas is heavily fortified. But at the JSA, the frontier is marked only by a low concrete divider and is typically peaceful despite ongoing hostility between the two sides.

It has also been a popular tourist site, with hundreds of visitors touring the South Korean side each day.

But South Korean tours were suspended after a US soldier ran across the border into the North in July. Travis King was released by North Korea in September and later charged with desertion by the US Army.

The tours partially restarted last month but were quickly suspended over security concerns after North Korea rearmed its troops, according to Yonhap news agency.

In 2017, a North Korean soldier drove a military jeep and then dashed on foot across the demarcation line at the JSA.

The defector was shot multiple times by his fellow North Korean soldiers but survived.

In 1976, two American soldiers were killed in the JSA by North Koreans with axes in a dispute over a tree.