South Korea called on its northern neighbor Wednesday to release a 50-year-old Christian missionary arrested while on an illegal trip to the reclusive state - with the South apparently emboldened by the surprise release of an American citizen from North Korea just hours earlier.

"Our government once again calls on [North Korea] to free the missionary and repatriate him," unification ministry spokesperson Lim Byeong-cheol said at a press briefing - referring to Kim Jung-wook, who was sentenced to a life of hard labor after being accused of spying and establishing underground churches following his arrest last October.

Lim insisted that Seoul "will make constant efforts, in cooperation with the international community, so that [Kim] will return to the arms of his family."

The briefing came after the United States announced the release of 56-year-old Jeffrey Fowle, who had been held in North Korea since April after leaving a Bible in a hotel - other reports claim his arrest was in May and that the Bible was left in a nightclub.

It was not immediately clear whether Fowle's release demonstrated an attempt by Pyongyang to improve ties with Washington.

"It is hard to gauge the North's intention for the move, and it remains to be seen how the North deals with the two other American detainees," a high-ranking official at Seoul's foreign ministry told local news agency Yonhap - speaking of Kenneth Bae and Matthew Miller.

Bae and Miller are serving hard labor sentences of 15 and six years, respectively.

Korean-American Christian missionary Bae is the North’s longest-serving U.S. detainee – having been taken into custody in 2012 on suspicion of unspecified anti-state crimes.

The motives of Miller – who was sentenced for “hostile” acts - remain unclear, but he is understood to have torn up his visa and attempted to claim asylum in North Korea after his arrival in April.

U.S. nuclear envoy Glyn Davies last month described the Americans' imprisonment in North Korea as a "serious impediment" to improved relations with Washington.
The U.S. State Department advises its citizens not to make even organized tours of the North, reflecting Pyongyang's record of punishing activities deemed lawful elsewhere - such as carrying out religious missions.

South Korean nationals are barred from travelling to North Korea without permission - the two sides are still technically at war despite the Korean War coming to an effective close in 1953.

Anadolu Agency