SEOUL - South Korea on Wednesday protested against a "unilateral sentencing" by the Democratic People's Republic of Korea (DPRK) of two South Korean detainees to hard labor for life.

Unification Ministry spokesman Lim Byeong-cheol told a press briefing that the DPRK conducted "unilateral" legal procedures against the two South Koreans, dismissing the verdict as " unacceptable."

The comments came after the DPRK's highest court sentenced Kim Guk-gi, 60, and Choe Chun-gil, 55, Tuesday to life imprisonment for hard labor for subversion of the country, espionage and illegal entry.

The DPRK's Korean Central Television reported that Kim and Choe admitted to all crimes, including collecting secrets on the highest leadership, political party, state and military, which were the hostile actions sought by the United States and South Korea.

In March, the DPRK said at a press conference in Pyongyang that Kim and Choe had been arrested on charges of spying for South Korea's National Intelligence Service (NIS).

The spokesman also urged Pyongyang to release two other South Koreans detained in the DPRK as well as Kim and Choe, saying the South Korean government was making efforts to encourage the DPRK to set free the detainees by cooperating with the international community.

The other two detainees were Joo Won-moon, a 21-year-old student who was arrested by DPRK border guards on April 22, and Kim Jung-wook, a missionary who was sentenced in 2014 by a DPRK court to hard labor for life.