SEOUL - North Korea said on Tuesday it had detained a U.S. citizen who entered its territory, apparently confirming a report that an American activist crossed into the state to raise awareness about Pyongyang's human rights abuses.

Robert Park, 28, walked over the frozen Tumen river from China and into the North last Friday, other activists said. He told Reuters ahead of the crossing that it was his duty as a Christian to make the journey and that he was carrying a letter calling on North Korean leader Kim Jong-il to step down.

A U.S. citizen illegally entered the country across the North Korea-China border and has been detained. The person is currently undergoing questioning by a related agency, the North's official KCNA news agency said.

KCNA offered no further details. It usually imprisons the few foreigners who cross illegally into the hermit state.

A U.S. State Department official in Washington said: We've seen the reports but have no positive confirmation that he's been detained.

A senior Obama administration official said the United States had asked Sweden -- which looks after U.S. interests in the country -- to seek information. Washington does not have diplomatic ties with Pyongyang.

North Korea may try to use Park as a bargaining chip with the United States in their high-stakes negotiations over the North's nuclear ambitions, analysts said.

In August, former U.S. President Bill Clinton went to North Korea to win the release of two U.S. journalists who were held by the state for about four months for suspected illegal entry, in a high-profile visit that paved the way for direct U.S.-North Korean nuclear talks.

Park, a Korean-American, had told Reuters he would not seek U.S. help.

I don't want President Obama to come and pay to get me out. But I want the North Korean people to be free, Park last Wednesday said before departing for China.

Until the concentration camps are liberated, I do not want to come out. If I have to die with them, I will. (For) these innocent men, women and children, as Christians, we need to take the cross for them, he said.

PREPARES TO DIE

I am going in for the sake of the lives of the North Korean people. And if he (Kim Jong-il) kills me, in a sense, I realize this is better. Then the governments of the world will become more prone to say something, and more embarrassed and more forced to make a statement.

Western governments and rights activists say North Korea keeps a network of political prisons, with more than 100,000 people jailed, to crush the possibility of dissent. Brutality is the norm and deaths are commonplace.

Pyongyang uses arbitrary killings and holds public executions to intimidate the masses. It prevents free speech, controls all media and crushes nascent attempts at reform by executing or imprisoning those who oppose the state, critics say.

Park was quoted by activists who went with him to the border as shouting when he went across: I am an American citizen. I am bringing God's love. God loves you.

The activists say they filmed him going across and have been trying to sell the video.

The U.S. journalists who were detained were Euna Lee and Laura Ling of U.S. media outlet Current TV. They were arrested in March working on a story near the border between North Korea and China.

The two said they crossed into the North by accident and were taken into custody in China by North Korean guards who chased them back across the border. (Additional reporting by Christine Kim in Seoul and Paul Eckert and Jeff Mason in Washington; Editing by Dean Yates)

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