WASHINGTON, March 16 (Xinhua) -- U.S. commanders in Iraq have requested another army brigade on top of five already on the way, which will bring the planned expansion of U.S. forces so far to close to 30,000 troops, the Boston Globe reported Friday.

    The request, which has not yet been announced, will involve between 2,500 and 3,000 more soldiers and dozens of transport helicopters and powerful gunships, according to the report.

    Just a week ago, U.S. President George W. Bush announced that about 4,700 support troops will join the 21,500 he ordered in January.

    If the latest request is approved, the total number of additional troops could reach 30,000.

    They are in addition to the estimated 130,000 troops already in Iraq.

    "This is the next shoe to drop," said a senior Pentagon official closely involved in the war planning.

    "But you cannot put five combat brigades in there and not have more aviation guys, military police, and intelligence units," he added.

    The additional troops designated for the "surge" are expected to be in Baghdad and western Anbar province by May.

    The Congressional Budget Office predicted last month the total surge could ultimately double in size and cost, once all support troops are in place.