The U.S. government called Wednesday for North Korea to release an American citizen jailed there, saying Washington's top priority is to secure the safety of its nationals.

"We urge the DPRK (North Korea) authorities to grant Mr. Bae amnesty and immediate release," Patrick Ventrell, deputy spokesman for the State Department, told reporters. "There is no greater priority for us than the welfare and safety of our U.S. citizens abroad."

The 44-year-old Korean-American man, Kenneth Bae, was arrested in November for unspecified anti-North Korea acts. He was reportedly working as a tour operator but multiple sources say he was involved in missionary work.

He was sentenced to 15 years of compulsory labor, and the U.S. has taken issue with the transparency of the communist nation's judicial process.

North Korea announced Tuesday Bae has begun life at a "special prison." The U.S. has been trying to win the freedom of Bae through the Swedish Embassy in Pyongyang, which acts as a "protecting power" for U.S. citizens in North Korea.

The U.S. has no diplomatic office in North Korea as they have no formal diplomatic ties.

Swedish authorities said they have no news about efforts to get Bae freed.

"We are present there and also helping a lot of other countries, but I don't have an update on these talks (on Bae),"

Swedish Prime Minister Fredrik Reinfeldt said at a joint press conference with Secretary of State John Kerry in Stockholm earlier this week.

The Bae issue is expected to be high on the agenda when Robert King, the U.S. special envoy for North Korean human rights, travels to Seoul next week.

Meanwhile, the U.S. remained noncommittal about an ongoing trip by a high-profile Japanese official to Pyongyang.

Isao Iijima, special counselor in charge of crisis management in the Shinzo Abe administration, arrived in the North Korean capital on Tuesday. His surprise trip is seen as aimed at discussing the issue of Japanese citizens abducted by the North decades ago.

The State Department spokesman said Washington is working closely with Tokyo on the matter.

In the early 2000s, Iijima is said to have helped arrange then-Japanese Prime Minister Junichiro Koizumi's trips to Pyongyang for talks with then-North Korean leader Kim Jong-il on the abduction issue.

During Koizumi's 2002 trip, Kim admitted that North Korean agents had kidnapped 13 Japanese citizens in the 1970s and 1980s to use them as language instructors for communist spies.

Pyongyang allowed five of them to return home, claiming the others were dead. Japan wants to confirm their fate. (Yonhap News)