A US tour operator has been sentenced to 15 years' hard labour in North Korea for unspecified crimes against the state.

NK News reports that Kennet Bae, owner of Nation Tours company, was arrested in November 2012 in Rason Special Economic Zone, North Korea's far north-eastern region, near the border with China and Russia.

He was accused of committing "crimes aimed to topple the DPRK" according to Korean news agency KCNA.

However, South Korean rights groups have suggested that authorities were upset because Bae, a devout Christian, repeatedly took pictures of starving children in the streets - called kotjebi or flowering swallows - and public executions of dissenters.

Bae was born in South Korea but is a naturalised American citizen. He will likely serve the sentence in a special facility for foreigners, not in the 200,000-strong forced labour camps.

He is not the first American to be detained in North Korea in recent years. Journalists Laura Ling and Euna Lee were sentenced to 12 years' hard labour in 2009 after illegally crossing the border from China while making a documentary about defectors. They were freed after Bill Clinton flew to Pyongyang to negotiate their release.

Other reports state that Bae is a missionary from the Ohio-based Christian Joseph Connection group.

North Korea uses the release of high-profile American prisoners to extract a form of personal tribute. The latest sentence could be utilised as a bargain in talks with Washington.

With its extremist blend of Marxism, nationalism and the cult of the ruling Kim family, North Korea is one of the most isolated states on earth.