It was not clear what the air force intends to do with the bombs, which are most effective against troops or tanks in open areas.

"What we were told today is that they are on the way," said the defense official, who asked not to be identified.

He said several were being shipped to the Gulf region.

MOAB stands for Massive Ordnance Air Blast, but it is known informally as the "mother of all bombs."

Developed by the Air Force Research Laboratory at Eglin Air Force Base in Florda, where it was tested last month, the bomb is a larger version of the 15,000 pound "daisy cutter."

The "daisy cutter" was used in Vietnam to clear jungle for helicopter landing pads, in the 1991 Gulf War to clear minefields and in Afghanistan to clear caves and strike fear into al-Qaeda and Taliban fighters.

The MOAB has a satellite guidance system and a tail kit to steer it to within about 13 meters (14 yards) of its target.

It is too big to be dropped normally. It is dragged out of the back of a C-130 cargo plane by a parachute.

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