"Some 23 million compatriots in the North are still groaning under dictatorship and repression, worse than Japan's past colonial rule," it said.
"South Korean taxpayers' money has returned as [North Korean] nuclear weapons and missiles, but few raise this problem."
Hwang Jang-yop has been named
chairman of the group [AP]
North Korea staged missile tests in July and a nuclear test in October.
Hwang Jang-yop, the highest-ranking defector to the South, has been named chairman of the group.
Hwang was secretary of the ruling Workers' party before defecting in 1997. He is now a leading critic of Kim Jong-il, the North Korean leader.
About 10,000 North Koreans have defected to South Korea in the past 50 years - 1,600 last year alone.
Hundreds of thousands are estimated to be hiding in China awaiting a chance to go to South Korea.
The group estimates that there are 400,000 North Korean refugees in China and elsewhere.