WASHINGTON, Dec. 14, 2004 -- There appears to be an almost endless supply of fighters willing to die for their cause in Iraq. Suicide bombers have routinely struck U.N. buildings, hotels and checkpoints since the end of major combat in the country.
The weapon of choice is usually an explosive-packed automobile, but explosive vests have been used as well. U.S. intelligence officials say the majority of the bombers are not foreign fighters, as many believe.
"The big myth is that there's an endless supply of suicide bombers, that the foreign fighters are everywhere. That's the story everybody wants to hear, and Iraqis don't want to admit that some of [the suicide bombers] might be Iraqis," said Brig. Gen. John Custer, director of intelligence for U.S. Central Command.
Just today, a suicide car bomber killed seven people at a Green Zone checkpoint in Baghdad. It was the second attack in two days near the same gate into the district that houses Iraq's interim government and the U.S. Embassy, officials said.
The recent assault on the former insurgent stronghold of Fallujah, U.S. military-led raids on private Iraqi homes and military bombings that have killed Iraqi civilians have radicalized young Iraqis.
"The deaths of their own families, the destruction of their homes -- all these are leading to frustration and anger and hopelessness, and they want the enemy to feel the same frustration and hopelessness, so they are resorting to this violence," said Muqtedar Khan, visiting fellow in foreign policy studies at the Brookings Institution and an expert in political Islam.
But it also appears that not all of the bombers are willing participants. U.S. military officials have found body parts in vehicles used in suicide bombings -- left by the frantic people who were trapped inside, unable to flee.
"What we've found in a number of places are hands chained to a steering wheel," Custer said. "We found a foot roped into the car unable to escape."
He said in some cases, it appeared that men were forced to carry out suicide bombings because their families were being held hostage.
"We've seen a number of incidents where -- wives [and] children kidnapped -- [the] fathers forced to drive a car, even so far as to have a car following it with a remote," Custer said.
And U.S. commanders say they are seeing a new tactic in the field -- insurgents sending two suicide bombers to launch an attack, in case the first one backs out.
ABC News' Martha Raddatz filed this report for "World News Tonight."