A group in a statement distributed to the media on Tuesday afternoon threatened to blow up the plane Lee is taking.

Lee Hee-ho, the widow of former President Kim Dae-jung, received a terror threat a day before her scheduled departure for North Korea on Wednesday.

"Lee Hee-ho along with her husband, Kim Dae-jung supported North Korea's Kim dynasty with South Korean people's tax money 15 years ago," the statement said.

"She helped the vicious regime acquire nuclear weapons in addition to prolonging its life. In this way, she has kept prolonging the pain of our compatriots in South and North Korea."

Police searched the budget airliner Lee was supposed to board, but no explosives were found. Lee took off for Pyongyang on Wednesday morning and will back in Seoul on Saturday.