U.s. forces in Iraq are launching a new crackdown on weapons smuggling from Iran, in part by tighter monitoring of border crossings, a U.S. commander told The Associated Press on Friday.

The effort is aimed at smugglers who, according to Maj. Gen. Michael Oates, supply Shiite extremist groups — mainly in Baghdad — with rockets, missiles, mortars and assembled explosive devices that have killed many U.S. troops.

"We're going to start squeezing this network pretty hard," said Oates, who leads a contingent of 19,000 U.S. troops in regions south of the capital as commander of the Army's 10th Mountain Division.

"We think we can actually have some success interdicting blatant smuggling by making sure the Iraqi people see that this stuff is being brought in and it's not helpful," the general said. To date, however, neither the U.S. nor its coalition partners have succeeded in intercepting weapons crossing the border, he said.

Asked about the timing, Oates said the improved overall security situation in Iraq "allows us to deal with this last remaining major threat, which is the Iranian lethal support" of Shiite extremist elements that U.S. officials term "Special Groups" to differentiate them from members of Shiite cleric Muqtada al-Sadr's Mahdi Army.

Oates said that much of the smuggled weaponry comes into Iraq through Maysan province, which borders Iran and has an official frontier crossing, called Sheeb, east of the city of Amarah.

He said Amarah, which was recently cleared of Shiite extremist forces by the Iraqi army, long was a hub for the shipment of smuggled weaponry from Iran; the arms would move from Amarah toward Baghdad either by heading west or by moving south to the Basra area and then north to the capital.

Oates also disclosed in the interview that among the stored weapons the Iraqi army has uncovered in Amarah since entering the city in force in mid-June were more than 2,200 mortar rounds, nearly 600 rockets, nearly 1,000 artillery rounds, 22 missiles and 141 of the most deadly version of the roadside bomb.

U.S. forces, which have not operated in Maysan province recently, intend to set up a patrol base not far from the border, Oates said.

U.S. forces, along with a group of civilians that includes some retired FBI agents and U.S. customs enforcement agents, will work with Iraq's border enforcement squads to tighten passport screening, cargo inspection and other border actions, Oates said.

The intent is to take a comprehensive approach up and down the border with Iran, the general said.

"If you block at one (crossing), then they'll move to another, so we're looking to develop a coherent strategy across that entire border," he said. U.S. forces already have set up a patrol base not far from a border entry point called Zurbatiyah in Wasit province, and they plan to take similar actions with regard to the Shalamcheh border crossing station in the southern province of Basra, Oates said.

Oates made clear that the intention is to take aggressive action inside Iraq, not across the border. He said it appears that most, if not all, of the weapons smugglers are Iraqis, although their networks begin in Iran.

The U.S. government has a wider variety of intelligence capabilities than Iraq to apply to this mission.

"We are beginning to understand the smuggling network," Oates said. "We will interdict it, with the Iraqis, and if we discover it's Iranian munitions, we're going to advertise it." If successful, such efforts would add a new level of credibility to U.S. assertions that Iran is fueling violence inside Iraq, he said.

For much of the war, U.S. and Iraqi forces were focused mainly on Al Qaeda and other insurgent forces that threatened to plunge the country into all-out civil war. Shiite extremist groups inside Iraq took advantage of that narrow focus to develop a network of weapons supply routes from Iran, he said.

"Now that Al Qaeda is hurt very badly, we're able to shift our emphasis and take a look at this other threat — and this is a significant threat that these Iranian-based extremist groups are attempting" carry out, not only by killing American troops but also seeking to topple the Iraqi government, he added.