I am shocked that American troops will face new rocket-propelled bombs in Iraq

Suspected Shiite militiamen have begun using powerful rocket-propelled bombs to attack U.S. military outposts in recent months, broadening the array of weapons used against American troops.

U.S. military officials call the devices Improvised Rocket Assisted Munitions, or IRAMs. They are propane tanks packed with hundreds of pounds of explosives and powered by 107mm rockets. They are often fired by remote control from the backs of trucks, sometimes in close succession.

Rocket-propelled bombs have killed at least 21 people, including at least three U.S. soldiers, this year.

The latest reported rocket-propelled bomb attack occurred Tuesday at Joint Security Station Ur, a base in northeastern Baghdad shared by U.S. and Iraqi soldiers. One U.S. soldier and an interpreter were wounded in the attack.

U.S. military officials say IRAM attacks, unlike roadside bombings and conventional mortar or rocket attacks, have the potential to kill scores of soldiers at once. IRAMs are fired at close range, unlike most rockets, and create much larger explosions. Most such attacks have occurred in the capital, Baghdad.

The use of the rocket-propelled bombs reflects militiamen’s ability to use commonly available materials and relatively low-tech weaponry to circumvent security measures that have cost the U.S. military billions of dollars.

To combat roadside bombs, known as improvised explosive devices or IEDs, U.S. and Iraqi troops have set up scores of checkpoints throughout the capital, increased patrols and purchased hundreds of armored vehicles that can resist such attacks.

Militia members and insurgents have at times increased the sophistication of their weapons, but the rocket-propelled bombs are makeshift devices that also have been used in recent years by insurgents in Colombia. Propane tanks are ubiquitous in Iraq, where the fuel is widely used for cooking, making it hard for security forces to stop production of the bombs.

To counter the threat posed by rocket-propelled bombs, soldiers have stepped up patrols around outposts, fortified their buildings and offered tens of thousands of dollars for information about networks that use the weapon.

Most attacks have been carried out during the day and some have been videotaped and aired on the satellite television station operated by Hezbollah, a Lebanese militia and political movement. U.S. military officials said they have found Iranian-made 107mm rockets at some of the blast sites, which they said suggests the weapons — or parts — may have come from Iran.