North Korea has cancelled its invitation to a US envoy who was to have sought the release of an American citizen it holds prisoner.

News of the planned trip by US diplomat Robert King had raised hopes that Kenneth Bae, a 44-year-old American who has been prisoner in North Korea since November, might be released.

King had been due to fly to Pyongyang on Friday, but State Department spokeswoman Marie Harf said on Friday that the visit had been cancelled after North Korea rescinded its invitation.

"We are surprised and disappointed by North Korea's decision," she said.

Harf said Washington had asked North Korea to explain its actions and that the US side would push for a new date, but that King was planning to fly back from Tokyo on Saturday.

"We remain gravely concerned about Mr Bae's health and we continue to urge the DPRK authorities to grant Mr Bae special amnesty and immediate release on humanitarian grounds," she said, referring to North Korea by its official initials.

'Inflammatory' material

Bae, a Korean-American tour operator whose Korean name is Pae Jun-ho, was arrested in November 2012 as he entered the northeastern port city of Rason.

North Korea, which strictly bans religious proselytising, said Bae was a Christian evangelist who brought in "inflammatory" material.

He was sentenced to 15 years hard labour on charges that he was trying to topple the regime of Kim Jong-un.

His family and US officials say he is now very sick, and have called for his release as a humanitarian gesture.

North Korea has in the past freed detained Americans after visits from high-level emissaries such as former presidents Bill Clinton and Jimmy Carter.

Bae was tried at a time of high tension between the US and North Korea over the latter's nuclear weapons programme. North Korea carried out its third nuclear test earlier this year and threatened to strike the US, but tensions have since eased.

America has been cool to North Korean overtures to restart talks, saying it is only interested in sitting down if Pyongyang commits to giving up its atomic weapons.

But releasing Bae, something the US has been seeking for months, could help foster goodwill between the rival nations.

Source: AFP