An appeals court on Thursday sentenced a 34-year-old man to one year in prison for threatening to blow up a plane that took South Korea's former first lady took to Pyongyang.

Upholding a lower court's decision, the Seoul High Court suspended the sentence for the man, identified only by his surname Park, for two years.

He was accused of sending a one-page letter to local journalists, threatening to blow up the plane of Lee Hee-ho, the widow of former South Korean President Kim Dae-jung, when she traveled to North Korea in August 2015.

The appeals court said he is guilty of obstructing official duties. Over 100 officers were mobilized to inspect the airport and planes for about five days before and after Lee's departure.

"The suspect seems to have been aware that his action could interfere police's normal execution of duties," the court said.

Lee, a symbolic figure for inter-Korean reconciliation due to her late husband's accomplishments, returned home on Aug. 8, after a four-day trip to the North.

President Kim, who died in 2009, was the architect of the "sunshine" policy that actively pushed for cross-border exchanges and reconciliation. He held the first inter-Korean summit with then North Korean leader Kim Jong-il in 2000. At that time, Lee accompanied her husband to Pyongyang. (Yonhap)