WASHINGTON - The US State Department on Thursday urged the Democratic People's Republic of Korea (DPRK) to immediately release a US citizen who was sentenced to 15 years of compulsory labor by its court.

"There is no greater priority for us than the welfare and safety of US citizens abroad, and we urge the DPRK authorities to grant Mr. Bae amnesty and immediate release," said State Department spokesman Patrick Ventrell at a briefing, referring to the sentenced American, identified by Washington as Kenneth Bae and by Pyongyang as Pae Jun Ho respectively.

"We've had longstanding concerns about the lack of transparency and due process in the North Korean legal system," he told reporters. "So now that Mr. Bae has gone through a legal process, we urge the DPRK to grant him amnesty and immediate release."

Ventrell's statement came after the Supreme Court of the DPRK rendered the verdict earlier the day. DPRK's official KCNA news agency said Thursday that Pae Jun Ho, the defendant, was arrested while "committing hostile acts against the DPRK" after entering Rason City as a tourist on November 3 last year.

From Jan 7 to 10, Former US New Mexico Governor Bill Richardson and Google Executive Chairman Eric Schmidt paid a " private humanitarian" visit to Pyongyang, which was reportedly linked to the release of Bae.

However, Richardson did not elaborate on whether he met Bae or not while commenting the private trip as "a productive and successful one."