"They hope to reschedule it soon but we don't have a firm date," said Jake Swenson, a spokesman for the Air Force Research Laboratory at Eglin Air Force Base in Florida.

The test would have been only the second of the MOAB, which was first tested March 11 and rushed into service for the war in Iraq. Several of the weapons were shipped to the Gulf region in April, a Pentagon official said at the time.

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

It is similar to the 15,000 pound "daisy cutter," which was used to raze jungle for helicopter landing pads in Vietnam, to clear minefields in the first Gulf war and more recently to blow out caves in Afghanistan.

The test was supposed to check out the reliability of the bomb's components and to certify for use in an MC-130 Combat Talon 1 aircraft, which is used by special operations forces. The first test certified it for use on an MC-130 Combat Talon 2 aircraft.

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 so big it has to be dragged out of the back of a C-130 cargo plane by a parachute.

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