WASHINGTON, April 5 (Reuters) - The U.S. Defense Department is preparing to send another 12,000 National Guard combat troops to Iraq, NBC Nightly News reported on Thursday, citing Pentagon sources.

New orders awaiting the signature of Defense Secretary Robert Gates will put 12,000 National Guard troops on alert to prepare to deploy be Iraq, the report said.

Four Guard combat brigades from units in four states would be involved in the involuntary mobilization, NBC said.

The one-year combat deployment would begin early in 2008, the report said.

The Pentagon referred queries about the report to the National Guard, where a spokesman had no immediate comment.

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