North Korea's supreme court sentenced American student Otto Warmbier, who was arrested while visiting the country, to 15 years of hard labour for crimes against the state, China's Xinhua news agency reported on Wednesday.

Warmbier, a University of Virginia student, was detained by the North in January for trying to steal an item bearing a propaganda slogan from his hotel in Pyongyang and had confessed to crimes against the state, North Korean media said previously.

Warmbier, who is from Wyoming, Ohio, and was 21 at the time of his arrest, told a media conference in Pyongyang last month that his crime "is very severe and pre-planned."

He was at the end of a five-day New Year's group tour of North Korea when he was delayed at airport immigration before being taken away by officials, according to the tour operator that had arranged the trip.

Warmbier had blamed a church in Ohio for his actions, saying a "deaconess" had offered him a used car worth $10,000 if he could present a US church with the slogan as a "trophy" from North Korea, the country's news service KCNA said.

The deaconess also said the Friendship United Methodist Church in Ohio would pay his mother $200,000 if he was detained by the North and did not return, KCNA quoted Warmbier as saying.

The church's senior pastor has denied knowledge of the deaconess named by North Korean officials and said Warmbier is not a member of the church.

North Korea has a long history of detaining foreigners and has used jailed Americans in the past to extract high-profile visits from the United States, with which it has no formal diplomatic relations.

North Korea is also holding a Korean-Canadian Christian pastor it sentenced to hard labour for life in December for subversion.

It has previously handed down lengthy sentences to foreigners before freeing them.

In 2014, North Korea released three detained Americans.

Former Governor Bill Richardson of New Mexico, who had previously traveled to North Korea, met the North's ambassador to the United Nations on Tuesday to press for the release of Warmbier, the New York Times reported.

"I urged the humanitarian release of Otto, and they agreed to convey our request," Richardson was quoted as saying.

Additional reporting by Reuters.