North Korea has blown up a liaison office set up to improve communications with the South in a row over defectors’ plans to send anti-Pyongyang propaganda leaflets across the heavily armed border. South Korea’s unification ministry said the North had set off an explosion at the joint liaison office at 2:49 pm, in the North Korean border town of Kaesong. The reports, from the Yonhap news agency, added that military sources had heard an explosion and seen smoke rising from the building. North Korea conformed in a statement carried by the official KCNA news agency that it had “tragically ruined” the office with a “terrific explosion”. It said the building’s destruction had come “in the wake of cutting off all communication liaison lines between the North and the South”. The move reflected “the mindset of the enraged people to surely force human scum and those, who have sheltered the scum, to pay dearly for their crimes” KCNA added, in an apparent reference to North Korean defectors in the South. North Korea appears to have acted on a warning by Kim Yo-jong, the increasingly influential sister of the country’s leader, Kim Jong-un, to destroy the “useless” office. “Before long, a tragic scene of the useless North-South joint liaison office completely collapsed would be seen,” she said on Saturday. The office opened in September 2018 to facilitate inter-Korean co-operation following successful talks between Kim Jong-un and the South Korean president, Moon Jae-in. Earlier on Tuesday, Pyongyang had warned it was “fully ready” to send troops into the demilitarised zone separating it from South Korea if defectors went ahead with their leaflet plans. The general staff of the Korean People’s Army [KPA] said on Tuesday it had been studying an “action plan” to re-enter zones that were demilitarised under a 2018 inter-Korean agreement and “turn the front line into a fortress and further heighten military vigilance against the South”. “Our army will rapidly and thoroughly implement any decisions and orders of the party and government,” it said in a statement carried by the KCNA. The KPA also said North Korea would send its own propaganda into the South as part of a “large-scale leaflet-scattering struggle against the enemy”. Leaflets critical of Kim Jong-un and his regime’s record on human rights have become a source of tension between the two Koreas in recent weeks. North Korea severed inter-Korean hotlines – an important point of contact between the two governments – and threatened to permanently close the Kaesong industrial complex, once a symbol of inter-Korean economic co-operation. Some experts believe the North is using the leafleting campaigns to pressure the South into reviving joint economic projects amid reports of food shortages in Pyongyang, and to communicate its anger at the lack of progress in nuclear talks with the US. These have stalled since a second summit between Kim and Donald Trump in March 2019 broke down over disagreements on sanctions relief. “The leaflets are an excuse or justification to raise the ante, manufacture a crisis, and bully Seoul to get what it wants,” said Duyeon Kim, a senior adviser at the International Crisis Group. Pyongyang feels betrayed by Seoul’s prediction that the US would lift some sanctions in exchange for North Korea closing its nuclear reactor site, and is angry that leaflets and US-South Korea military drills continue, Duyeon Kim said. “They’re upset that Seoul has done nothing to change the environment and is again telling Seoul to stay out of its nuclear talks with Washington,” she added. Tuesday’s warning suggests North Korea is prepared to send soldiers into border areas where Kim and Moon agreed to cease “all hostile acts” during their first summit in September 2018. “I regret that North Korea-US and inter-Korean relations have not made progress as expected,” Moon said this week in a message to mark the 20th anniversary of the first inter-Korean summit, between Kim Jong-il and Kim Dae-jung. “But what’s most important is trust, which the South and North should build through constant dialogue.” Several defector groups in South Korea regularly send flyers, along with food, $1 bills, mini radios and USB sticks containing South Korean dramas and news, usually by balloon over the heavily fortified border. In response, South Korea’s government has filed a police complaint against two defector groups, saying their activities were not helping “efforts to achieve peace and prosperity of the Korean peninsula”. Human Rights Watch accused Seoul of submitting to North Korean threats. “It is shameful how President Moon and his government are totally unwilling to stand up for the rights of North Koreans,” Phil Robertson, the group’s deputy Asia director, said in a statement. “Instead of proposing a blanket ban on sending balloons with messages and materials to the North, President Moon should publicly demand that North Korea respect freedom of expression and stop censoring what North Koreans can see.” The defector groups, however, said they would go ahead with plans to send leaflets across the demilitarised zone – which has divided the Korean peninsula since the end of the 1950-53 Korean war – later this week.