A Christian missionary has been sentenced to 10 years in one of North Korea's punitive hard labour camps for alleged "unpardonable espionage".

Kim Dong Chul, aged 62, who was born in South Korea and is a naturalised US citizen was accused of stealing information, including military secrets, and passing it on to South Korea.

North Korean state news agency KCNA reported: "The accused confessed to all crimes he had committed and gathered and offered information on its party, state and military affairs to the South Korean puppet regime, which are tantamount to state subversive plots and espionage," according to Reuters.

At a press conference in March in Pyongyang, Dong Chul, who lived in Virginia in the United States, appeared to confess. Foreign prisoners are often forced to confess in North Korea. He told reporters he had been paid by intelligence officers from South Korea and that he had been introduced to them by US intelligence.

Before Dong Chul was arrested last October, he had set up a business in a part of Rason in North Korea that is set aside as a special economic zone.

Earlier this year, a woman who saw him on television recognised him as a Christian missionary who she had seen give testimony in the US about the work he was doing in North Korea. A pastor also recognised him as the same man.

He has asked both the US and South Korea for help. He is one of six foreigners known to be held by North Korea, where as many as 70,000 Christians are currently imprisoned in labour camps. About 300,000 of North Korea's 25.3 million population are believed to be Christian. Open Doors ranks the country in first place on its persecution watch list.

North Korea did its fourth nuclear test in January and has also done recent nuclear missle tests, breaching UN sanctions. Last Thursday, an emergency meeting of the UN Security Council was called after two mid-range ballistic missiles crashed after they were launched. A fifth test is believed imminent.