With Al Qaeda falling away, U.S. forces in Iraq are turning their attention to another front: the Iranian border. They aim to crack down on weapon smuggling from Iran by tightening the frontier with Iraq's neighbor to the east, a U.S. commander told The Associated Press on Friday.

The effort is aimed at smugglers who supply Shiite extremist groups 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 Maj. Gen. Michael 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.

U.S. troops will establish small outposts in the vicinity of two or three official border crossings and seek to build relations with local tribes whose cooperation is critical, the general said. One such outpost already is set up.

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" to carry out, he said, not only by killing American troops but also seeking to topple the Iraqi government.

Oates called the weapons smuggling from Iran "the last remaining major threat" to be handled for Iraq.

As for the overall state of the Iraq war, Oates said "security is the best we've seen it" in his part of the country. But he said he would counsel against deciding on further U.S. troop reductions until after Iraq's provincial elections, which are scheduled for October. He said the outcome would go a long way in determining whether the security gains of the past year can hold up with a smaller U.S. presence.

In Washington on Friday, the White House said the United States and Iraq had agreed to seek "a general time horizon" for further reductions in American combat troops in the country. As violence has decreased, Iraqi officials have been pressing the U.S. to agree to a timeline to withdraw U.S. forces.

In Iraq, Oates said he doesn't expect to stop the smuggling from Iran, only to lessen the movement of weaponry.

"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. U.S. officials term those elements "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 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 roadside bombs.

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.

The U.S. troops, along with American civilians who include retired FBI agents and 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 at crossings up and down the border with Iran, the general said.

"If you block at one, 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 an 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.

He 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.