Unification Minister Kim Yung-ho on Friday called on North Korea to "immediately and unconditionally" send a detained South Korean missionary and five other nationals back home, condemning the North's yearslong arbitrary detention as grave human rights violations.

South Korea's top point man on North Korea issued a rare statement marking 4,000 days after missionary Kim Jung-wook was arrested in Pyongyang in 2013. He was sentenced to hard labor for life on charges of spying for South Korea's spy agency.

In 2014, two other South Korean missionaries -- Kim Kook-kie and Choi Chun-gil -- were also detained in North Korea on similar charges. Three former North Korean defectors, who had obtained South Korean citizenship, were held captive in 2016.

"The ROK government condemns North Korea's illegal and inhumane human rights violations and strongly urges the North, which is a party to major international human rights instruments, to immediately and unconditionally release our nationals who are illegally detained," Kim said in the statement, using the acronym of South Korea's official name -- the Republic of Korea.

The minister strongly denounced North Korea for unreasonable and excessive sentencing of the six individuals without a fair and public trial; its failure to provide basic procedural justice upon arrest and during detention; and the continued arbitrary detention.

"North Korea must not ignore our legitimate demands concerning the lives and safety of our citizens and must clearly recognize the seriousness of the issue, as well as the international community's strong warnings against its repeated violations of universal human rights norms," he said.

Kim also vowed efforts to bolster cooperation with the international community to resolve the issue of South Korean abductees, detainees and prisoners of war (POWs), and ensure that Japanese abductees and individuals from other countries no longer fall victim to the North's human rights abuses.

Separately from the six South Korean detainees, 516 South Koreans have yet to return home among an estimated 3,835 people who were kidnapped by North Korea after the 1950-53 Korean War.

At least 60,000 POWs are also estimated to have not come back home or gone missing after being detained in North Korea. A total of 80 POWs have returned home since 1994, but only nine were alive as of March.