An American tourist has been sentenced to 15 years of hard labour in North Korea for attempting to steal a propaganda banner.

Otto Warmbier, a University of Virginia student, was convicted of subversion and sentenced following a one-hour trial on Wednesday at North Korea's Supreme Court.

Warmbier was arrested as he tried to leave the country in early January. He was in North Korea with a New Year's tour group.

Before the trial, the 21-year-old from Wyoming, Ohio, said he had tried to steal a banner as a trophy for an acquaintance who wanted to hang it in her church.

The court held that he had committed a crime "pursuant to the US government's hostile policy toward (the North), in a bid to impair the unity of its people after entering it as a tourist".