An American Christian missionary who has been detained in North Korea for more than a year should serve out his sentence, Pyongyang's top envoy to Britain said, in a remark suggesting that the isolated country may not free him anytime soon.

Kenneth Bae was arrested in November 2012 while leading a group of tourists. He was accused of unspecified anti-state crimes and sentenced to 15 years of hard labor, though he has been hospitalized in recent months due to illness.

North Korea's ambassador to Britain, Hyun Hak-bong, said in a video interview posted Thursday that Bae would be freed when he serves out his prison term.

"When he finishes his term according to the law, there is no reason not to release him," Hyun said in the interview with Sky News, a 24-hour news channel in Britain.

He also said there are occasions for pardon in the North, though he said he "cannot predict that Kenneth Bae will be pardoned or not. He should finish his term. That is all."

His comments came more than a week after Bae called for pardon and asked the U.S. government to help secure his freedom. Bae made the comments during his first meeting with reporters in Pyongyang in early January.

In late January, U.S. Secretary of State John Kerry met with Bae's family in Washington.

The U.S. has offered to dispatch Amb. Robert King, special envoy on North Korean human rights issues, to Pyongyang to negotiate Bae's release, but the North has been unresponsive, according to U.S. officials.

In recent years, several U.S. citizens were detained in North Korea, and all but Bae were released later.

In 2009, former U.S. President Bill Clinton flew to Pyongyang to win the release of two American journalists caught during a reporting tour covering North Korean defectors near the border with China.

Meanwhile, Hyun said Jang Song-thaek, the once-powerful uncle of North Korean leader Kim Jong-un, was shot to death. 

The North said it executed Jang in December on charges of treason though it did not specify the exact manner in which he was executed. Hyun said "no" when he was asked by Sky News about media reports that Jang might have been fed to dogs.

"He was shot to death," Hyun said, adding he had no information whether Jang's family members were also executed as reported in some media.

Hyun dismissed as "political propaganda by our enemies" the media reports of execution of Jang's family, calling them a "fabricated report that doesn't deserve my comment."

In late January, multiple sources said all relatives of Jang, including children and the country's ambassadors to Cuba and Malaysia, have also been executed. (Yonhap)