Iraqi militia fighters are being trained in Iran to build and use deadly armor-piercing roadside bombs and complex attack strategies against American forces, the US military said. US military spokesman Maj. Gen. William Caldwell would not say how many militiamen had gone to Iran but said that questioning of fighters captured as recently as this month confirmed many had been in Iranian training camps. "They do receive training on how to assemble and employ EFPs," Caldwell said Wednesday, adding that fighters also were taught how to carry out attacks that use explosives followed by assaults with rocket-propelled grenades and small arms. EFP stands for explosively formed penetrator. The weapon causes great uneasiness among US forces because it explodes with tremendous force and can penetrate heavily armored vehicles with a fist-size lump of molten copper. In January, US officials said EFPs had killed at least 170 American soldiers in Iraq. "We know that they are being in fact manufactured and smuggled into this country, and we know that training does go on in Iran for people to learn how to assemble them and how to employ them. We know that training has gone on as recently as this past month from detainees' debriefs," Caldwell said at a weekly briefing. The general would not say specifically which arm of the Iranian government was doing the training but called the instructors "surrogates" of Iran's intelligence agency. He also said the US military had evidence that Iranian intelligence agents were active in Iraq in funding, training and arming Shi'ite militia fighters. Caldwell opened the briefing by showing photographs of what he said were Iranian-made mortar rounds, RPG rounds and rockets that were found in Iraq. The accusations are the latest attempt by the United States to show that Iran is meddling in the Iraq war. If true, the training poses a serious threat to both US forces and Iraqi stability. Iraq, which like Iran is majority Shi'ite, has found itself in a difficult position since the US-led invasion in 2003, trying to maintain good relations with its neighbor while not angering the Americans. Commanders of a splinter group inside the Shi'ite Mahdi Army militia have told The Associated Press there are as many as 4,000 members of their organization that were trained in Iran and that they have stockpiles of deadly roadside bombs known as EFPs. Asked for reaction, Caldwell said he could not confirm the number. The Mahdi Army commanders who spoke to the AP did so on condition of anonymity because their organization is viewed as illegal by the American military and giving their names would likely lead to their arrest and imprisonment. They said Iran's elite Revolutionary Guards was running the training operation in Iran.