North Korea said on Wednesday it had sentenced an American man to eight years of hard labour for illegally entering the country.

Aijalon Mahli Gomes "admitted all the facts" when he appeared at the central court in Pyongyang on Tuesday, the official Korean Central News Agency (KCNA) reported.

Representatives from the Swedish embassy, which represents US interests in North Korea, were allowed "as an exception" to attend the trial, the agency said.

The 30-year old from Boston was also fined 70 million won, equivalent to about 700,000 dollars at the official exchange rate.

Gomes, a former English teacher in South Korea and reportedly a devout Christian, was arrested in January -- the fourth US citizen in less than a year to be detained for illegal entry.

"His guilt was confirmed according to the relevant articles of the criminal code of the DPRK (North Korea) at the trial," KCNA said.

"The accused admitted all the facts which had been put under accusation. The presence of representatives of the Swedish embassy here to witness the trial was allowed as an exception at the request of the Swedish side protecting the U.S. interests," KCNA said.

The U.S. State Department had no immediate comment. Washington does not have formal diplomatic ties with North Korea.

Agencies