'Block-Buster' Truck Bomb One of the Biggest Ever 61,500 lb. bomb, more than 10x Oklahoma City explosive, found in Afghanistan.

Nov. 13, 2013 -- Afghan national security forces near the border with Pakistan recently intercepted one of the largest truck bombs ever built, a massive "vehicle-borne improvised explosive device," or VBIED, packed with some 61,500 pounds of explosives.

By comparison, the truck bomb that all but leveled the Alfred P. Murrah Federal Building in Oklahoma City on April 19, 1995, killing 168 people, was comprised of almost 5,000 lbs. of ammonium nitrate fertilizer mixed with fuel oil. The same recipe is commonly used in Afghanistan to make a variety of IEDs that have killed hundreds of ISAF troops in small numbers since 2001 -- but typically using dozens of pounds, not thousands.

"We're talking something with the power to raze whole blocks in an American city," Andrew Gumbel, author of last year's "Oklahoma City: What the Investigation Missed -- And Why It Still Matters," told ABC News.

Army Col. Christopher Garver, a spokesperson for the U.S.-led International Security Assistance Force's Joint Command in Kabul, told ABC News the massive bomb was discovered Oct. 14 when the truck was stopped in Gardez, Afghanistan. The bomb, he said was, in the military's estimation, "larger in comparison to some others we have seen." Another Defense Department source said that it was one of the largest truck bombs ever known to have been built.

"Vehicle-borne IEDs are one of the most significant threats to everyone in Afghanistan, as we have seen over the summer fighting season," Garver said.

As another point of reference, the TNT truck bomb that destroyed the U.S. Marine compound in Beirut 30 years ago, killing 241 American troops, was about one quarter the size of the Gardez VBIED.

Afghan and U.S. sources linked the recent Hino "jingle" truck, a local variety of cargo truck, piled with TNT to the al Qaeda-aligned Haqqani network, which allegedly has been responsible for almost all major truck bombings in Kabul and in Afghanistan's eastern tribal areas near Pakistan, from which the insurgents originate. A likely target was the U.S. military's Forward Operating Base Goode near Gardez City, the sources told ABC News.

Afghanistan's National Directorate of Security (NDS) said the explosives were "placed professionally under firewood" in the Hino truck.

Garver said the truck bomb, which an NDS video showed stopped on a desolate road and loaded with white bags, was intercepted by Afghan security forces. According to Afghan sources, the driver was a Pakistani who set off a grenade in the cab of the truck. He was taken to a nearby hospital where he detonated a suicide vest and killed himself, officials said.

The Haqqani network was designated a terrorist organization by the U.S. State Department in September 2012, a move that was "welcomed" by the U.S. military.

An ABC News investigation, which aired on "World News with Diane Sawyer" this week, showed that lawmakers have tried to stop the U.S. Army from giving logistics contracts to companies linked to Afghan insurgents including the deadly network run by Jalaluddin Haqqani and his son Siraj.

The Special Inspector General for Afghanistan Reconstruction, John Sopko, has called for cancelling the contracts because classified intelligence links the contractors to the Haqqani insurgents, who are responsible for killing hundreds of American G.I.s.

On Monday, Siraj's brother Nasiruddin was reported to have been assassinated in Islamabad, Pakistan.

The CIA has long gauged the effectiveness of military assaults on Haqqani leadership on both sides of the border by their ability to use large bombs in eastern Afghanistan and Kabul. Haqqani attacks have not subsided over the years.

U.S. and other NATO alliance forces who make up ISAF, as well as U.S. Special Operations Forces, have long faced casualties from Taliban bombers trained by al Qaeda who attack troops with suicide vests, car bombs and pressure-plate IEDs.

Since 2001, 934 American troops have been killed and almost 12,000 wounded by IEDs in Afghanistan, according to the military's Joint IED Defeat Organization.

But massive truck bombs are rare -- and one carrying more than 30 tons of explosives would be unusual anywhere in the world, experts said. Some analysts questioned the Afghans' estimate of the explosives' weight but still acknowledged the size of the Gardez VBIED is extraordinary.

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