A senior U.S. military spokesman says Iranian forces have infiltrated Iraq to provide training, money and equipment to Shi'ite extremists and fuel their insurgency. The officer went farther than others have in detailing Iran's alleged role in Iraq's violence.

Brigadier General Michael Barbero

U.S. officials frequently criticize Iran for supporting Iraqi Shi'ite extremists. But in the past they have declined to say whether that support includes infiltration by Iranian forces. At a news conference Wednesday, Brigadier General Michael Barbero made that direct connection.

"I have seen reports of their involvement and presence there as trainers to train these terrorists and extremist groups," he said.

General Barbero, an operations officer on the staff of the top U.S. generals, also says Iran is providing technology to help Iraqi insurgents build more effective bombs, what the military calls Improvised Explosive Devices, or IEDs.

"I think it's irrefutable that Iran is responsible for training, funding and equipping some of the [Shi'ite] extremist groups, and also providing advanced IED technology to them," he said. "And there's clear evidence of that."

The bombs are the insurgents' most effective weapons, accounting for more than half of the more than 2,500 U.S. military deaths in Iraq, and thousands of Iraqi civilian casualties.

General Barbero says coalition troops have not directly encountered any of the Iranian forces he says have been inside Iraq, and he would not provide any details on the number or specific duties of the Iranians.

Asked what the U.S. military is doing to fight the Iranian influence in Iraq, he said it is mainly a political challenge, but there is at least one thing the military can do.

"Militarily, in the execution of this operation to neutralize the [Shi'ite] extremist groups, we'll go a long way to removing their direct influence into the affairs of the sovereign country of Iraq," noted General Barbero.

General Barbaro also criticized Syria for allowing fighters and supplies to flow into Iraq from its territory, but he did not say anything about Syrian forces being involved. He said the coalition is working with Iraq's new government to further improve security along all the country's borders.

The general also spoke about the decision announced Tuesday to activate up to 2,500 U.S. Marines who are now on reserve status to help in the wars in Iraq and Afghanistan. He says the move will enable commanders to fill jobs in certain military specialties that are running short of personnel because of the two wars. He says all of those called will be within the seven years of combined active and reserve duty for which they originally volunteered.

General Barbero also disputed a reporter's suggestion that the activation indicates things are not going well in Iraq. He says the effort to establish security in Baghdad is having notable success, and that the United States still hopes to be able to reduce its troop presence in Iraq by the end of this year.