North Korea has blown up sections of roads and rail lines on its side of the heavily fortified border with South Korea, further ratcheting up tensions on the Korean peninsula.

About midday on Tuesday (local time), some northern parts of the roads and rail lines connected to the south were blown up, the Joint Chiefs of Staff said in a message 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 cut off the unused inter-Korean roads and railways and further fortify the areas on its side of the border.

Seoul had warned on Monday that North Korea was getting ready for a detonation.

It follows an escalating war of words between the Koreas after the north accused the south of sending drones over its capital Pyongyang.

Last Friday, North Korea 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.

The sister of North Korean leader Kim Jong-un, Kim Yo Jong, blamed “military gangsters” from the south for the drone infiltration, and said those involved would pay the price.

The north had installed landmines and barriers along the border. On Monday, heavy equipment was seen doing more work, South Korea’s JCS said.

The south ramped up surveillance and readiness following 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.

South Korea spent about 180 billion won ($200 million) in taxpayers’ money to rebuild the inter-Korean road, according to the Yonhap news agency.

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

The Unification Ministry in South Korea condemned the explosions as “highly abnormal” and “regressive”, and said they violated earlier agreements.

On Monday, Kim oversaw 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.

Last January, Kim ordered the abandonment of all plans for peaceful unification between the two states. He labelled his southern neighbour as the “invariable principal enemy”.

-with AAP