Members of an anti-North Korea civic group release balloons containing leaflets denouncing the North's leader Kim Jong-un towards North Korea, at Imjingak pavilion in Paju (Reuters)

A group of South Korean activists have sent anti-Pyongyang leaflets across the North Korean border, despite the communist regime earlier threatening a "merciless military strike" in the event of such action.

Closely watched by about 100 security officers, the activists floated about 50,000 leaflets in seven balloons from a park near Paju, just a few kilometres from the North Korean border, AFP reported.

The balloon carried pictures of famous past dictators such as Saddam Hussein, Muammar Gaddafi and Nicolae Ceausescu accompanied by a message urging North Koreans to stand up against the Pyongyang dictatorship and its new supreme leader Kim Jong-un.

Before the launch, the activists - many of whom are defectors from North Korea - scuffled with some local residents who feared Pyongyang's retaliation.

Last week South Korean authorities prevented leafleting from taking place in the city of Paju, after North Korea had threatened a military response if the leaflets were to be floated across the border.

"The moment a minor movement for the scattering is captured... a merciless military strike by the Western Front will be put into practice without warning. The surrounding area will become targets of direct firing of the KPA [Korean People's Army]," North Korean military officials said to the state news agency KCNA.

"The KPA never makes empty talk."

Although it was not the first military intimidation by the North over anti-regime propaganda from the South, the message worried Seoul because of its unusual specificity. The time and location of the threated strike were given, together with advice to evacuate the area.

However Pyongyang took no action a few days later, when members of another activist group - Fighters for Free North Korea - floated a further 200,000 leaflets to North Korea form a hill in Gimpo, Gyeonggi Province, a few kilometres south of Paju. The balloons also carried $1 bills.

"We're just sending information about what North Korean defectors saw and felt in South Korea to our families back there in the form of letter. It is an infringement of our freedom of expression if the government tries to stop us. It's nonsense to say that this will spark a war," Fighters for Free North Korea leader Park Sang-hak told Korean newspaper Chosun Ilbo.

North Korea has not opened fire on the South's mainland territory since the 1950-53 Korean War. However tension between the two nations remains high, as Seoul believes Pyongyang is seeking ways to influence South Korea's presidential election in December.

The North opposes South Korea's current government led by Lee Myung-bak because of its hardline strategy towards Pyongyang.

A member of an anti-North Korea civic group holds a leaflet denouncing the North's leader Kim Jong-un, at Imjingak pavilion in Paju (Reuters)
A Paju resident holds onto a door of an anti-North Korea civic group's vehicle after the group released balloons containing leaflets denouncing the North's leader Kim Jong-un towards North Korea, at Imjingak pavilion in Paju (Reuters)