North Korea says it is holding an American tourist for "violating" its laws. The man has been named as Jeffrey-Edward Fowle, who is said to have entered the country on April 29th.

The North's KCNA news agency said he is being questioned for "conduct inappropriate for the purpose of his visit as a tourist".

Reports in Japan said that he had been detained in the middle of last month - just before he was due to leave the country - for having left a Bible in his hotel.

A US State Department official said Washington was aware of the reports.

"There is no greater priority for us than the welfare and safety of US citizens abroad" the official said.

Three US citizens are now thought to be held in North Korea. The other two were arrested after arriving on tourist visas and accused of crimes against the State.

Kenneth Bae has been in custody for 18 months while the second man has been held since April.

Pyongyang has arrested a number of US citizens in the past few years, reportedly using them as a way of getting visits from high-profile figures, including former President Bill Clinton.

North Korea and the outside world - particularly the US - have tense relations, with Pyongyang accusing the US of conspiring to overthrow its leadership.

For its part, the US is worried about North Korea's nuclear and missile programmes.

The US State Department has urged its citizens to avoid North Korea because of the "risk of arbitrary arrest and detention" even while holding valid visas.

"Foreign visitors to North Korea may be arrested, detained, or expelled for activities that would not be considered criminal outside North Korea" it said.

The US has no diplomatic ties with North Korea and the interests of its citizens in the country are represented by Sweden, which has an embassy in Pyongyang.