The U.S. officials said weapons were smuggled into the country by the Quds Force, an elite unit of the Iranian Revolutionary Guard that U.S. officials believe is under the control of Iran's supreme religious leader, Ayatollah Ali Khamenei. The officials in Baghdad said that Iranians recently detained in Iraq by U.S. forces belong to the Quds Force.

U.S. military officials in Iraq had previously described the use of "explosively shaped charges" to target vehicles, but Sunday's briefing was the first time they displayed pieces of what they called an "explosively formed penetrator" or EFP.
The one such device shown at the briefing was a cylinder of PVC pipe about eight inches long and about six inches in diameter. The officials said the devices are deadly because the explosion sends a slug of malleable metal, often copper, at velocities high enough to penetrate the armor of tanks and Humvees. Their components require precision machining that Iraq has shown no evidence of being able to perform, the officials said.

The first known attack using such weapons in Iraq occurred in May 2004, and the rate of attacks using them has nearly doubled in 2006, the officials said. They have also been used in southern Lebanon, the explosives expert said. The Lebanese Shiite organization Hezbollah receives military support from Iran.
The defense analyst said Iranians used Iraqi smugglers to bring the weapons into Iraq. "The smoking gun of an Iranian standing over an American with a gun, it's never going to happen," he said.

The officials said the weapons are often supplied to what the officials called "rogue" elements of the Mahdi Army, the powerful Shiite militia led by anti-American cleric Moqtada al-Sadr. One official said there was no "widespread involvement" of the Iraqi government in supplying the weaponry.

A group of Iraqis coming into southern Iraq from Iran were detained by Iraqi border forces in 2005, the defense analyst said, and "they had the materials, EFPs and whatnot, on them."

The officials provided further details on the case of two Iranians captured during a December raid on the compound of a leading Shiite politician, Abdul Aziz al-Hakim of the Supreme Council for the Islamic Revolution in Iraq, and five Iranians seized in the raid of a liaison office in the northern city of Irbil in January.

The raid at Hakim's compound netted Mohsen Chirazi, whom U.S. officials described as a high-ranking Quds Force operations chief, as well as documents with information about sniper rifles and mortars, the officials said. The senior defense official said that when U.S. officials discussed the allegations with Hakim's representatives, their explanation was that "it is normal for different groups to acquire armaments for protection purposes."