SEOUL - North Korea said on Tuesday it would put on trial two U.S. journalists arrested this month on its border with China, stoking tensions with Washington ahead of a planned rocket launch that has already alarmed the region.

The reclusive state accused the two women reporters, Laura Ling and Euna Lee from the U.S.-based media outlet Current TV, of unspecified hostile acts.

Pyongyang's announcement comes just days before North Korea plans to put what it says is a satellite into space but which Washington and others say will be a test of a long-range missile that could carry a warhead as far as U.S. territory.

One Seoul-based analyst said intelligence reports indicated North Korea appears to have built nuclear warheads for its mid-range Rodong missiles, which can reach Japan.

I have some intelligence assessments that indicate they have assembled nuclear warheads for Rodong missiles, said Daniel Pinkston, an analyst with the nongovernmental International Crisis Group. No one can know this with 100 percent accuracy.

Many proliferation experts believe the North, whose only nuclear test in 2006 was seen as a partial success, does not have the technology to miniaturize a nuclear device for a warhead. It might be able to place a biological or a dirty bomb, where radiation is spread through conventional explosives.

SUSPECTED HOSTILE ACTS

The reporters were arrested two weeks ago by the Tumen River, which runs along the east side of the border between North Korea and China, while working on a story.

The illegal entry of U.S. reporters into the DPRK (North Korea) and their suspected hostile acts have been confirmed by evidence and their statements, according to the results of intermediary investigation conducted by a competent organ of the DPRK, North Korea's KCNA news agency said.

The organ is carrying on its investigation and, at the same time, making a preparation for indicting them at a trial on the basis of the already confirmed suspicions.

A U.S. State Department spokesman said Washington was trying to solve the problem through diplomatic channels.

The incident comes amid growing pressure on the North not to launch its Taepodong-2 rocket.

Peter Beck, a Korean affairs specialist at the American University in Washington, said the arrests could provide a means for Pyongyang and Washington to talk to each other.

After the test and some hand wringing, we (the United States) will grope our way back to table. But we really don't know if the North is serious about negotiating at this point. It looks like they aren't, he said.

North Korea says the launch will be between April 4-8.

It is certain to feature on the sidelines of the G20 summit this week in London when U.S. President Barack Obama meets global leaders, including President Hu Jintao of China, the nearest the isolated North has to a major ally.

China has avoided directly criticizing Pyongyang, urging all sides to exercise restraint.

U.S. DEPLOYMENT

The United States, Japan and South Korea are deploying missile-interceptor ships in the area.

All have said they would shoot down the rocket if it threatened their territory and that the launch would be in violation of U.N. resolutions. Both houses of Japan's parliament passed a resolution urging North Korea not to fire the rocket.

Pyongyang has threatened to restart a plant that makes arms-grade plutonium if the United Nations does penalize it.

It also told Japan if it tried to shoot down the rocket that North Korea's army will consider this as the start of Japan's war of reinvasion more than six decades after the Second World War and mercilessly destroy all its interceptor means and citadels with the most powerful military means.

The prickly state already faces a range of U.N. sanctions for previous launches and its nuclear test in 2006, which added to concerns of potential instability in a region that accounts for one sixth of the world's economy.

Analysts say the North may not be worried by more sanctions from the launch, which it will see as a way of gaining greater leverage in negotiations with the outside world that is trying to make it give up attempts to build a nuclear arsenal.

A successful Taepodong-2 launch -- the first attempt in 2006 failed -- would be a huge boost at home for leader Kim Jong-il and also to his impoverished country's weapons exports, one of its few major sources of income from abroad.

The timing, analysts say, is important for the 67-year-old Kim, thought to be in poor health after a suspected stroke last year raised questions over his grip on the impoverished country.

(Additional reporting by Arshad Mohammed in Washington, Isabel Reynolds in Tokyo, Jack Kim, Jon Herskovitz and Kim Junghyun in Seoul, Editing by Dean Yates)

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