Before it started, 56-year-old Kim Yun-suk fell asleep to the hum of insects and woke to the chirping of birds. Now, she is kept awake every night by what sounds like the soundtrack of a low-budget horror movie at top volume. “The peaceful sounds of nature… have now been drowned out,” Kim told AFP. “All we hear is this noise.”

The campaign is the latest manifestation of steadily-declining ties between the two Koreas this year, which have also seen Pyongyang test ever more powerful missiles and bombard the South with trash-carrying balloons.

Since July, North Korea has been broadcasting the noises for huge chunks of almost every day from loudspeakers along the border. The northern point of Ganghwa – an island in the Han river estuary on the Yellow Sea – is only about two kilometres (a mile) from the North. When AFP visited, the nighttime broadcast included what sounded like the screams of people dying on the battlefield, the crack of gunfire, bombs exploding, along with chilling music that started at 11:00 pm.

Experts said the new broadcasts almost meet the criteria for a torture campaign. “Almost every regime has used noise torture and sleep deprivation,” Rory Cox, a historian at University of St Andrews, told AFP. “It is very common and leaves no physical scarring, therefore making it deniable.”

Exposure to noise levels above 60 decibels at night increases the risk of sleep disorders, experts said, but AFP tracked levels of up to 80 decibels late at night on Ganghwa during a recent trip.

“I find myself taking headache medicine almost all the time,” An Mi-hee, 37, told AFP, adding that prolonged sleep deprivation due to the noise has also led to anxiety, eye pain, facial tremors and drowsiness. “Our kids can’t sleep either, so they’ve developed mouth sores and are dozing off at school.” Distraught and desperate, An travelled to Seoul and got on her knees to beg lawmakers at the National Assembly to find a solution, breaking down in tears as she described the island’s suffering.

Choi Hyoung-chan, a 60-year-old resident, said the South Korean government had failed to protect vulnerable civilians on the frontier. “They should come here and try to live with these sounds for just ten days,” he told AFP, referring to officials in Seoul. “I doubt they could even endure a single day.”