South Korean activists on Monday said they will launch leaflets across the border denouncing North Korea and its ruling family to mark the birthday of late leader Kim Jong-Il this week.
They will float balloons carrying 200,000 leaflets towards the isolated state on Thursday when the North plans an elaborate celebration for its late leader.
South Korean activists and North Korean defectors have regularly sent anti-Pyongyang leaflets that have also carried news about outside world.
"We... will send letters for our North Korean compatriots to mark the birthday of the national traitor who enslaved the people through three generations," the Fighters for Free North Korea group, which is led by a defector, said in a statement.
"Jong-Un... is using his father's birthday to force North Koreans to pledge loyalty to him and to continue the family dictatorship," it said, referring to the North's new leader.
Kim died of a heart attack in December aged 69 after ruling the country for 17 years following the death of his father and founding president, Kim Il-Sung, in 1994.
The North swiftly proclaimed Kim's youngest son, Jong-Un, as the "great successor" and appointed him as the chief military commander.
Pyongyang's state media said top party and military officials as well as workers and troops have recently visited Kim's supposed birthplace to mark his birthday and to publicly reaffirm loyalty to the Kim dynasty and Jong-Un.
The North, which tightly controls news from outside, has angrily responded to the balloon launches and threatened to fire across the heavily-fortified border to stop them.