The US has called for the "immediate release" of Merrill Newman, an 85-year-old Californian detained in North Korea.
Newman, a Korean War veteran, was taken off a plane last month as he was about to leave the reclusive state after a tourist visit.
"Given Mr Newman's advanced age and health conditions, we urge the DPRK to release Mr Newman so he may return home and reunite with his family," National Security Council spokeswoman Caitlin Hayden said.
Hayden also urged Pyongyang to free another American, Kenneth Bae.
The 45-year-old tour operator arrested a year ago was sentenced to 15 years' hard labour on charges of seeking to topple the government.
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"Kenneth Bae has been in DPRK custody for over a year, and we continue to urge the DPRK authorities to grant him amnesty and immediate release," Hayden said.
"We remain deeply concerned about the welfare of the US citizens held in custody in the DPRK."
Earlier, North Korea for the first time officially admitted holding Newman, saying he has been detained for "hostile acts" against the communist country.
Newman was held after entering the North "under the guise of a tourist", the official KCNA news agency said.
The retired financial executive has been accused of infringing upon the "dignity and sovereignty" of the secretive state and "slandering its socialist system, quite contrary to the purpose of the tour", the report said.
North Korea, which has no formal ties with the United States, also released video showing Newman reading an apology confessing to his alleged crimes.
