Seoul officials said Tuesday they would work to stop human rights activists sending leaflets to North Korea by drone, as the remote-controlled aircraft could pose a security risk.

“Those caught using drones to carry anti-North Korean leaflets across the inter-Korean border from the South will be punished accordingly,” an official at the South’s Unification Ministry said.

The warning comes after South Korean activists have threatened to send up to 500,000 leaflets on the fifth anniversary of the sinking of the Cheonan navy ship by North Korea on March 26.

Activists have launched such leaflets to the North multiple times in recent months using balloons. Authorities had refused to stop the activists, saying their right to freedom of speech had to be respected.

But Seoul officials said the same principle could not be applied to activists sending off leaflets on drones, as they were a kind of human-controlled aircraft. Such devices cannot be allowed to fly over the militarized inter-Korean border without authorization, Seoul officials said.

The leaflets usually contain documents criticizing the Kim Jong-un regime, U.S. dollar bills, and chocolate goodies. Such materials will inform the oppressed citizens of the North about the outside world, activists in the South have asserted.

Most of them are former North Korean refugees who fled to the South. Some have suggested that U.S. human rights activists will join them in the potential leaflet send-off later this month.

By Jeong Hunny (hj257@heraldcorp.com)