SEOUL: An American has been detained for illegal entry into North Korea, Pyongyang's state media said Tuesday, in an apparent reference to a Christian rights activist who crossed the border last week.

"An American was detained after illegally entering the DPRK (North Korea) through the DPRK-China border on December 24," the Korean Central News Agency said in a one-paragraph report.

"He is now under investigation by a relevant organ."

Activist Robert Park was reported by colleagues to have crossed into the North on December 25, Christmas Day, in a one-man protest against repression in the hardline communist state.

They said he walked across the frozen Tumen River from China.

Park, a US citizen of Korean ancestry, claimed he had seen a vision from God of North Korea's liberation and redemption, his colleagues said, adding that he crossed the border shouting "I came here to proclaim God's love".

Park, from Tucson, Arizona, carried a letter calling for Pyongyang leader Kim Jong-Il to release political prisoners, shut concentration camps and take steps to improve rights and conditions, his colleagues said.

The US State Department Monday expressed concern that the North may have detained the activist.

It said Sweden, which represents US interests in Pyongyang in the absence of diplomatic relations, has offered to seek more information about Park's fate.

In March this year, two US journalists who crossed into North Korea from China while working on a story about human trafficking spent more than four months in jail for illegal entry.

Television journalists Laura Ling and Euna Lee were sentenced to 12 years' hard labour but were freed as part of a diplomatic mission spearheaded by former US President Bill Clinton in August.