PAJU, South Korea (Reuters/AFP) - A planned launch of balloons by South Korean activists to send leaflets to North Korea on Saturday with messages critical of its leader turned into a clash with residents of the border area, who said the move will threaten peace between the Koreas.

Hundreds of residents of the city of Paju near the heavily militarised border turned up in a show of force, many elderly farmers and some driving tractors aimed at blocking roads, to try and stop the launch of the leaflets by anti-North groups.

Local residents, some of whom have been camping out in the area, met a busload of activists and threw eggs at some of them, demanding they turn back and leave them to live in peace. "Things like this will trigger artillery firing at us," said Mr Kwon Soon Wan, 63, who said he was born and raised in the township of Munsan, which is the northern-most area of Paju, and runs a snack bar there. "Safety is top priority because it's our lives that are hanging in the balance," he added.

Mr Choi Woo Won, one of the activists pelted with an egg, said: "By the time our leaflets cover all of North Korea, murderer Kim Jong Un will perish and be destroyed."

But it was not clear whether the group would be able to go ahead with the planned launch of the leaflets, after activists who advocate engagement with the North sabotaged some balloons.

Mr Cho Sung Ho, a 66-year-old farmer who grows beans in a special area near the border where usual civilian access is limited, said the leaflets harm the South's national interest. "I want them to refrain. It will stop everything, like tourism here," he said, adding the political tension surrounding the leaflet campaign has also affected his farm work. "I want dialogue to solve the issues (between the Koreas), not this."

Several hundred police officers were on site, adding to the chaos in a normally quiet area visited by South Korean and some Chinese tourists.

The police intervened in the tense confrontation that began near a park in the border town of Paju, some 40km north of Seoul, when a dozen people with their faces hooded seized an activists' truck carrying balloons and leaflets.

Some 100 police officers surrounded a bus carrying around 20 activists after local residents hurled eggs at it, shouting: "Go back. Don't put our lives in danger!"

Local residents also set up road blocks with tractors and a placard reading "Stop anti-North leaflet launch jeopardising our lives!".

"We will become the victims of shelling if leaflets are scattered," read another placard put up in a tree.

The activists had planned to release balloons carrying around 40,000 leaflets criticising the North's government across the heavily militarised frontier.

They retreated after a two-hour protest during which they traded insults with the residents and chanted slogans such as "Let's terminate the dictatorship of (North Korean leader) Kim Jong-Un!".

However they did not abandon their attempt entirely, parking their bus on a road leading to the park with some insisting they should try again to float the balloons.

"Those instigated by North Korea had ambushed us to block our event today but we will come back," Busan University professor Choi Woo Won, the main organiser of Saturday's event, told reporters.

North Korea has threatened unspecified "military action" if the launch were to be allowed by the South Korean authorities and said it could scuttle planned inter-Korean talks aimed at easing tensions and improve ties.

Pyongyang has blamed the South Korean government for previous leaflet launches and has threatened to respond with military action.

The propaganda printed on the leaflets infuriates Pyongyang and has threatened to derail talks agreed between the two Koreas after the North sent a high-level delegation earlier this month, which was seen as its biggest peace overture in years.

The messages often single out the North's young leader Kim Jong Un, questioning his legitimacy to rule a country where people struggle with poverty while his family lives in luxury and scarce resources are channelled to arms programme.

Earlier this month the North fired machine guns at a balloon, launched by a defector, when it flew low across the border because it was short of gas.

The authorities in the South have urged activists to refrain from launching the leaflets on safety grounds, but say they can not legally stop them due to the constitutional freedom of expression.

The two Koreas remain technically at war because a truce was signed at the end of their 1950 to 1953 conflict not a peace treaty. More than 1.8 million troops are deployed on the peninsula, making it one of the world's most heavily armed hotspots.