North Korea has sentenced two South Korean nationals to life imprisonment on charges of espionage, its state media reported Tuesday, coinciding with the day the U.N. opened a field office in Seoul to monitor and study the repressive state’s human rights situation.

The North’s official Korean Central News Agency said that the North’s Supreme Court meted out life sentences to Kim Kuk-gi and Choi Chun-gil, who it said were arrested after spying on the regime “under the direction of the U.S. and South Korea.”

Seoul’s Unification Ministry expressed “strong regrets” over the rulings, criticizing them as going against the international humanitarian norms and calling for their immediate release.

“The North did not give any prior explanation whatsoever to our government and their families and took that illegitimate step,” the ministry said in a press release. “Our government would like to make it clear that we can’t accept the unilateral rulings.”

In March, the North invited foreign and local media outlets for a press conference during which it said that it had arrested the two, calling them “spies.”

At the news conference, the North claimed they collected secret documents from the North’s ruling Workers’ Party and military and state organizations under the direction or support of the U.S. and South Korean intelligence institutions, and that they attempted to spread the “capitalist bourgeois” way of life inside the reclusive state.

The sentencing came as the U.N. opened the field office to further pressure Pyongyang to improve its woeful human rights record. The North argued that with the office, the U.S., South Korea and others are trying to overthrow the regime by politicizing the human rights issue and interfering in domestic affairs.

By Song Sang-ho (sshluck@heraldcorp.com)