A South Korean fisherman has found a suspected North Korean drone near a frontline island south of the rivals' disputed sea border, military officials said.

The wreckage, without a wing, engine or camera, was recovered when it got caught in his net off Baengnyeong island, a South Korean defence ministry spokesman said.

"Its shape and colour were similar to those of the unmanned aerial vehicles discovered earlier," he said.

In March and April, South Korea retrieved crashed drones equipped with cameras in three different places, including Baengnyeong island and the northern border city of Paju.

Military officials said their memory chips contained pictures of border areas and the capital Seoul, including the presidential palace.

After a joint investigation with US experts, Seoul claimed to have secured "smoking gun" proof that the three recovered drones were flown from North Korea and had been pre-programmed to fly over South Korean military installations.

North Korea angrily denied any involvement and accused the South of "fabricating" the evidence.