Several Americans have been detained in North Korea in recent years [GALLO/GETTY]

North Korea said it will charge a US citizen detained since November with crimes against the nation, amid reports that he was engaged in missionary work in the hardline communist state.

A man identified as Jun Young-Su has been investigated "for committing a crime against the Democratic People's Republic of Korea [DPRK] after entering it", the official news agency said on Thursday.

"He admitted his crime in the course of investigation," it said, adding officials are preparing to bring charges against him.

The agency said Washington had been told of the arrest, and Swedish diplomats, who represent US interests in the capital Pyongyang, had been given access to the detainee.

The US doesn't have diplomatic staff in North Korea.

The US state department disclosed the detention on Tuesday and confirmed that Swedish diplomats had been given access. It gave no details of the individual, but appealed for the detainee's release on humanitarian grounds.

"We would call on the government of North Korea to release this citizen on humanitarian grounds and we would ask that they respect and treat this citizen in a manner consistent with international human rights law," Mark Toner, State Department spokesman, told reporters.

A source in Seoul familiar with North Korean affairs identified the man as a Korean-American businessman in his 60s who was detained for involvement in missionary work.

The man, who attends a church in Orange County, California, has been travelling frequently to the North disguising himself as a trader, the source said.

Arrests in the past

Several Americans have been detained in North Korea in recent years.

In August, former President Jimmy Carter brought home Aijalon Gomes, who had been sentenced to eight years' hard labour for crossing into the North from China.

Korean-American missionary Robert Park, who defiantly walked into North Korea on Christmas Day in 2009, was released weeks later without charge.

Also in 2009, journalists Laura Ling and Euna Lee were arrested for trespassing into North Korea and released only after former President Bill Clinton made a trip to Pyongyang to ask for their freedom.

The latest arrest came as Carter plans to travel to Pyongyang again as early as this month.