North Korea blows up parts of road to South, Seoul says

North Korea has blown up sections of inter-Korean roads and rail lines on its side of the heavily fortified border between the two Koreas, South Korea's military says, ratcheting up tensions on the Korean peninsula.

At about midday on Tuesday, some northern parts of the roads and rail lines connected to the South were blown up, the Joint Chiefs of Staff (JCS) said in a message sent to media.

In response, South Korea's military fired warning shots south of the military demarcation line dividing the neighbours, though the explosions had not caused any damage on Seoul's side of the border, it said.

The explosions came after Pyongyang pledged last week to completely cut off the inter-Korean roads and railways and further fortify the areas on its side of the border. Seoul had warned on Monday that the North was getting ready for a detonation.

The North has already been installing landmines and barriers along the border, and was seen on Monday doing additional work with heavy equipment, South Korea's JCS said.

The South had ramped up surveillance and readiness after the incident, it said.

The two Koreas are still technically at war after their 1950-53 war ended in an armistice, not a peace treaty.

The cross-border links are remnants of periods of rapprochement between the countries including a 2018 summit between the leaders when they declared there would be no more war and a new era of peace had opened.

Around 180 billion won ($A200 million) in taxpayers' money was spent by South Korea to rebuild the inter-Korean road, according to the Yonhap news agency.

There has been an escalating war of words between the Koreas after the North accused its rival of sending drones over the country's capital Pyongyang.

North Korea on Friday said the drones had scattered a "huge number" of anti-North leaflets, in what it called political and military provocation that could lead to armed conflict.

A spokesman for the South's JCS declined on Monday to answer questions over whether the South Korean military or civilians had flown the alleged drones.

North Korean leader Kim Jong-un had overseen on Monday a meeting with defence and security officials to discuss how to respond to the "enemy's serious provocation that violated the sovereignty of the DPRK", state media KCNA reported.

DPRK is short for the Democratic People's Republic of Korea, North Korea's official name.