South Korea said Wednesday it had found another crashed drone, days after a probe into three recovered unmanned aerial vehicles (UAVs) concluded they all came from North Korea.

The latest drone apparently crashed into a hill in the southern suburbs of Seoul where its wreckage was stumbled on by a passer-by, a defence ministry official said.

"An investigation team from a nearby military unit is at the site," the official told AFP.

It was not immediately clear when the drone may have crashed.

South Korea recovered three rudimentary UAVs in March and April in separate locations near its land and sea borders with the North.

The defence ministry said last week that a joint investigation with US experts had provided "smoking gun" proof that all three were flown from North Korea and had been pre-programmed to fly over South Korean military installations.

North Korea angrily denied any link with the drones, accusing the South of "fabricating" the evidence.