PAJU, South Korea (Yonhap) -- A group of North Korean defectors on Saturday in the city of Paju sent leaflets across the border via balloon with anti-Pyongyang messages, leading to a clash with progressive civic activists opposed to their actions.

At 11 a.m., about 50 North Korean defectors released 10 huge balloons carrying 200,000 leaflets, 1,000 U.S. $1 bills and 500 pamphlets detailing the development of South Korea from Imjingak pavilion near the border.

Defectors said their action, which took place on the birthday of the late North Korean Kim Jong-il, was in response to North Korea's recent nuclear test.

"Despite strong opposition and condemnation by the international community, North Korea went ahead with the nuclear test, which runs counter to the peace of mankind," said Park Sang-hak, the head of the Fighters for Free North Korea (FFNK), a civic group of activists and North Korean defectors. "We wanted to let 20 million North Koreans know more about their country's nuclear ambitions and its hypocrisy."

About 30 minutes before the launch, a progressive civic group called the Solidarity for Peace and Reunification of Korea held a press conference and urged the defectors not to release the balloons.

In a press statement, the progressive group said, "Sending leaflets at a time of heightened tension following the North Korean nuclear test could only drive the Korean Peninsula into a state of war."

FFNK members voiced their disapproval, and it led to shouting matches that went on for about 10 minutes. Police forces prevented the situation from escalating further.

Last October, North Korea warned of a military strike if leaflets are sent across the border, forcing South Korean authorities to previously stop defectors from trying to fly balloons with anti-North Korean messages.