The leaflet drops are thought to have been a factor behind North Korea's announcement last week that it would close the frontier between North and South from December 1.

The announcement came after North Korean military officials protested to their South Korean counterparts over the leaflets.

South Korean officials have previously said there is nothing they can do to stop the activists, citing freedom of speech.

However, earlier this week officials at the South Korean unification ministry said they were looking at any possible legal avenues through which they could enforce a ban on the airdrops.