WASHINGTON, Feb 10 (Reuters) - The U.S. military stepped up its monitoring of North Korea this week amid concerns about a possible missile launch by Pyongyang, a U.S. military official said on Tuesday.

The official, who spoke on condition of anonymity, said the U.S. military decided on Monday to move "assets" including naval vessels into monitoring position in the Pacific. The official declined to provide further details.

U.S. Pacific Command, which is responsible for U.S. military interests on the Korean Peninsula, acknowledged that it was monitoring activities in North Korea but declined to comment on specific operations.

"We're watching those things closely with all the assets we have," Pacific Command spokesman Marine Major Bradley Gordon said. "We've got all sorts of sensors all around the area. But I won't say what or where they are."

Destitute North Korea has recently been posturing about a possible test-firing of its long-range Taepodong-2 missile as the result of an aid dispute with South Korea.

Some U.S. officials speculate that North Korea could be trying to draw international attention ahead of an upcoming trip to Asia by U.S. Secretary of State Hillary Clinton.

The Taepodong-2 has never flown but is designed for a range that could eventually hit U.S. territory. A 2006 test-firing of the Taepodong-2 failed when the missile exploded seconds after its launch.

U.S. officials said they were unaware of any recent evidence to suggest that North Korea was actively preparing for a missile launch.

Defense Secretary Robert Gates on Tuesday played down the notion that any Taepodong-2 launch would pose a danger to the United States.

"Since the first time that they launched the missile -- it flew for a few minutes before crashing -- the range of the Taepodong-2 remains to be seen. So far, it's very short," Gates told reporters at a Pentagon briefing.

"It would be nice if North Korea would focus on getting positive messages across to its negotiating partners about verification and moving forward with the denuclearization," he said.

Sputtering talks to end North Korea's nuclear arms program have been stalled for months, with Pyongyang complaining that promised aid is not being delivered under an agreement reached with China, Japan, Russia, South Korea and the United States.

Experts say the North lacks the technology to miniaturize a nuclear weapon and mount it to a missile warhead. (Reporting by David Morgan, editing by Vicki Allen)

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