South Korean police said Friday they would stop a planned launch of anti-North Korean leaflets across the tense border, after Pyongyang threatened to retaliate.

A group of defectors from the North had said they would float 200,000 leaflets over the heavily militarised frontier by balloon on Saturday to protest Pyongyang's dire human rights record.

Local residents, however, oppose such action because the North has threatened to shell sites used to launch leaflets, which carry messages such as calls for an uprising against the communist regime.

"In order to prevent possible clashes between the activists and residents there, we've decided to stop the vehicle (loaded with leaflets) from coming near the launch site," a police spokesman told AFP.

The South's Yonhap news agency said the authorities planned to mobilise 500 riot police to block access roads to Imjingak, the planned launch site.

Pyongyang on Wednesday warned it would not stand idle if the launch went ahead, condemning the plan as an "intolerable provocative act" aimed at tarnishing the North's image and insulting its dignity.

Activist Park Sang-Hak said the group would consider postponing the launch at the government's request. Police stopped a similar launch by the same group on April 13.

The government asked them to delay the new action until it reaches a deal with the North to ensure the return of seven workers remaining at a joint industrial zone that has become a casualty of military tensions.

South Korea had been due to pull out all its workers from Kaesong on Monday but the seven remained to settle unresolved issues such as unpaid taxes and wages for North Korean workers, believed to amount to millions of dollars.

The talks were continuing on Friday and it was unclear whether the workers would return by the end of the day, Seoul's Unification Ministry said.

Tension has been high since the North, angered by fresh UN sanctions sparked by its nuclear test in February and South-US military drills, issued a series of apocalyptic threats of a nuclear war against Seoul and Washington.