Kenneth Bae, a tour operator arrested in November 2012, made a public confession of wrongdoing -- often seen as a prerequisite for the totalitarian state to release foreign prisoners.
State Department spokeswoman Jen Psaki yesterday said the United States remained "very concerned" about Bae's health and was "actively" working to release him.
"We continue to urge the DPRK authorities to grant Bae amnesty and immediate release," Psaki said, referring to the North by its official name, the Democratic People's Republic of Korea.
The official said that Robert King, the US envoy on human rights in North Korea who has visited in the past, was prepared to bring home Bae.
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"We have offered to send Ambassador King to Pyongyang to secure Mr. Bae's release. We have asked the North Koreans this, and await their early response," the official said.
Bae, a Korean American also known as Pae Jun-Ho, was arrested as he entered North Korea's northeastern port city of Rason. He was sentenced to 15 years of hard labor last year on charges of seeking to topple the government.
Bae admitted to wrongdoing and called on the US government to help secure his release so that he could return to his family "at the earliest possible date," according to Kyodo.
A court in North Korea, which strictly controls religion, had described Bae as a militant Christian evangelist who had smuggled subversive material into the country and sought to establish a base in Rason.