BAGHDAD, Iraq — In the latest attempt to link the deadliest form of roadside bombs in Iraq to components manufactured in Iran, U.S. Army officers yesterday displayed plastic explosives they said were made in Iran and recovered during a raid Saturday in violence-racked Diyala Province.

An Army explosives expert said the C-4 plastic explosives were used to make lethal bombs which the military calls EFPs — explosively formed projectiles. The explosives were found alongside enough bomb-making materials to build 150 EFPs capable of penetrating heavily armored vehicles, according to the expert, Major Martin Weber.

Mortars and rockets found in the same cache also were manufactured in Iran, Major Weber said. The cache included 150 machine-milled copper plates that form a shaped, concave lid on the projectile. When the weapons explode, those lids form balls of molten metal that can punch through the armor on vehicles.

The cache was believed to be the first EFP manufacturing site found inside Iraq, officers said. They had previously assumed that most EFPs were assembled outside the country and brought in nearly whole.

Officers said they did not know where the copper plates were manufactured, or by whom. They also said they could not prove who supplied the materials or who was building the EFPs.

The briefing was the third in two weeks in which American military officials set forth evidence that they said showed Iran’s hand in Iraq’s violence. By contrast with previous sessions, officers at yesterday’s display were careful not to accuse the Iranian government of involvement. American officials have had to backtrack from previous assertions of direct involvement by Iran’s top government officials.

“I don’t think there’s any way for us to know if it’s tied to any government,” said Major Jeremy Siegrist, executive officer for the unit that recovered the materials. “That’s a stretch too far.”

But by summoning reporters to the display and providing Major Weber as an on-site expert to assert that some items came from Iran, the military was clearly emphasizing the linkage to that country.

Major Weber said cutting, stamping, and milling the copper plates requires technical expertise, as does arming and triggering the EFPs. He said Iran has the necessary expertise. That country provides weapons and technical support for Hezbollah, which has used similar explosive devices in southern Lebanon.

Referring to the C-4, rockets and mortars, Major Weber said, “you can establish the country of origin, and that is a fact.”

Captain Clayton Combs, the company commander whose 1st Cavalry unit recovered what officers called “an IED factory,” using the military acronym for improvised explosive devices, or roadside bombs, said he found it “interesting” that explosives, rockets and mortars from Iran were including among EFP-making materials. Asked to elaborate, Captain Combs replied, “I’m not willing to go beyond that.”

A cache of EFP materials found by American forces in Hillah, south of Baghdad, last week was probably a transit point for materials to be assembled elsewhere, Major Weber speculated. The Hillah cache — and many others found by American troops — included C-4 explosives made in Iran, Major Weber said.

Mortars and rockets are commonly used in other types of IEDs. The rockets and mortars found in Diyala, a troubled province north of Baghdad, were manufactured in 2006 and 2002, respectively, officers said, meaning they were not left over from the Iran-Iraq war in the 1980s.

EFPs have killed at least 170 American troops, according to American officials. So far, 3,156 American troops have died in Iraq.

The Bush administration is mounting a campaign to isolate and discredit Iran over its nuclear program and its role inside Iraq. It has accused the Al Quds Brigade, a unit of Iran’s Revolutionary Guard, of supporting Shiite attacks against American forces in Iraq.

Major Siegrist said American troops were tipped off about the bomb site in Diyala by a local resident. The materials were hidden inside two freezers and a water container buried in a palm grove.

The cache included plastic plumbing pipes that formed EFP housings, along with metal rings used to secure the devices. Also found were detonation cord, blasting caps, fuses, voltage regulators, and ball bearings.

On display Monday was a fully formed EFP, which Captain Combs said had been found at the site, fitted with a C-4 charge. The device was the size and shape of a large coffee can. It was fitted with what Major Weber said was a metal sighting device for aiming at a target. It was topped with a copper plate, or disk, the size of a bread plate.

EFPs cause more damage than other types of IEDs because of “the density and speed of 2 to 4 pounds of metal [copper] traveling at an extremely high rate of speed,” Major Weber said.

Also recovered from the Diyala site were fifteen 122-mm rockets, two dozen 120-mm mortar rounds, mines, anti-aircraft ammunition, and rocket-propelled grenades, Captain Combs said.

The most significant items were the copper plates, made from 5-mm copper sheets, he said.