A Seoul court on Friday sentenced a pro-North Korean activist to four years in prison for making an unauthorized trip to the communist country.

Ro Su-hui, the vice-chairman of the South Headquarters of the Pan-national Alliance for Korea's Reunification, was found guilty of illegally visiting North Korea by way of China in March of last year, in violation of the National Security Law.

The Seoul Central District Court also ordered that his rights, such as suffrage, be stripped for three years after his release from prison.

During his 104-day trip, the 69-year-old attended a memorial service for Pyongyang's former leader Kim Jong-il and took part in various propaganda events. He returned to the South in July by walking across the border at the village of Panmunjom, which separates the two Koreas.

"The Constitution guarantees the freedom of expression and thoughts. However, the act of threatening the safety of the community cannot be approved," Judge Seoul Beom-shik said in his ruling.

In the same ruling, Won Jin-wook, the secretary general of the group, also received a three-year jail term for masterminding Ro's trip and colluding with North Korean spies from the Pyongyang branch of the organization.

South Korea's National Security Law prohibits citizens from visiting the North without prior permission or from praising the North.

Ro was the sixth person to return home through the border village after traveling to the North without South Korean government approval.

(Yonhap News)