SEOUL (AFP) - South Korean police on Saturday stopped a planned launch of anti-North Korean leaflets across the tense border, sparking an angry protest from activists, witnesses said.

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.

Police set up road blocks on access routes to the planned launch site at Imjingak, and stopped a pickup truck loaded with the leaflets, towing it to a nearby police station.

But the police allowed through roughly 50 people, including the defectors and other anti-North Korean activists from the United States, who gathered at Imjingak to protest.

"Let North Koreans know the truth," an activist said during a speech as others unfurled banners calling for an end to what they described as North Korea's "hereditary dictatorial regime".

Police had said Friday they would block the launch in order to prevent possible clashes between the activists and local residents. Police stopped a similar launch by the same group on April 13.

Local residents 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.

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 its image and insulting its dignity.

The police action coincided with a fresh warning from Pyongyang on Saturday that the fate of a joint industrial zone in the North hinged on Seoul.

"It is totally up to the puppet regime's attitude whether Kaesong industrial zone is closed for good or not", the North's official Committee for Peaceful Reunification of Korea said on its Internet website, Uriminzokkiri.

Pyongyang has repeatedly blamed the South for the deadlock over the Kaesong factory park, once a rare symbol of cross-border cooperation.

South Korea on Friday withdrew its last remaining workers from the complex, which is at risk of permanent closure due to soaring military tensions.

It is the first time that Seoul has pulled out all its workers from the flagship project since it was opened in 2004.

Tension has been high since the North conducted its third nuclear test in February, and issued a series of apocalyptic threats of war against Seoul and Washington in recent weeks.