North Korea has sentenced a US man to six years of hard labour for "hostile acts", according to reports.

Matthew Miller, 24, was arrested in April shortly after arriving in the country as a tourist, and was put on trial on Sunday morning for allegedly violating the terms of his tourist status.

Miller, of Bakersfield, California, is believed to have torn up his visa at Pyongyang's airport and demanded asylum, the Associated Press reported.

North Korean authorities did not specify Miller's exact charges, but said he intended to "experience prison life so that he could investigate the human rights situation".

After its brief session on Sunday morning, the court denied Miller an appeal to the sentence.

Missionaries arrested

An imminent trial is also expected to take place for US citizen Jeffery Fowle, 56, who was arrested in May for leaving a Bible at a provincial club after he entered North Korea as a tourist.

A third US national, Korean-American missionary Kenneth Bae, is currently serving a 15-year sentence of hard labour for alleged "hostile acts".

Miller, along with Fowle and Bae, recently appealed to the US government to send a representative to North Korea to negotiate their release. Washington subsequently appealed to Pyongyang to release the detained Americans out of "humanitarian concern".

Religious proselytizing is strictly forbidden in North Korea, and authorities have strongly cracked down on missionaries who have been accused of breaching local laws.

In 2009, US journalists Euna Lee and Laura Ling were arrested while covering a story on human trafficking at the border between China and North Korea.

The reporters were sentenced to 12 years hard labour for hostile acts and entering North Korea without a visa. They were pardoned later that year by the then North Korean leader Kim Jong-il after former US president Bill Clinton made an unofficial visit to the country.