South Korea has urged North Korea to immediately and unconditionally release six South Koreans from its custody.

In a statement issued Friday, the four-thousandth day of detention for missionary Kim Jung-wook, Unification Minister Kim Yung-ho said the six South Korean nationals have been unlawfully deprived of their freedom.

Strongly condemning the North’s actions and calling the continued detention arbitrary, the minister called on Pyongyang to listen to the international community and respect international human rights norms.

The North apprehended Kim Jung-wook in 2013, later convicting him of espionage and sentencing him to hard labor for life.

Missionaries Kim Kook-kie and Choi Chun-gil were taken into custody in 2014 on similar charges, and in 2016 the North apprehended three defectors who had acquired South Korean citizenship.