BAGHDAD, Iraq — U.S. and Iraqi forces struck back at insurgents yesterday, storming a cluster of northwestern towns in a region where 22 Marines have been killed this week.

The assault in violent Anbar province began before 6 a.m. as 180 Iraqi soldiers and 900 members of the 2nd Marine Division, backed by M1-A1 Abrams tanks, helicopters and jets bearing 500-pound bombs, stormed into Haditha, Haqlaniyah and other small towns along the Euphrates River where military officials believe insurgents are mustering to launch attacks. Iraqi Special Operations forces helped direct U.S. air strikes, according to a military news release.

The province has seen at least a half-dozen similar-size offensives by Marines since early May, most farther west along the Syrian border, where Marines have sought to stem the flow of foreign fighters and weapons into Iraq. But the insurgency has remained strong in the Sunni Arab-dominated region, where opposition to the U.S. presence runs deep.

"When we did operations out west, the insurgents moved to the Haditha-Haqlaniyah area," said Col. Bob Chase, the operations chief for the 2nd Marine Division. "That area is a geographic crossroads where they can get north to Mosul and east to Ramadi and Baghdad. It has good urban terrain for them to melt into. And we are well aware there are still plenty of ammunition supplies from the Saddam Hussein era for them to make use of."

The Marines were positioning for the initial stages of the operation Wednesday when 14 were killed as an amphibious assault vehicle struck a roadside bomb near Haditha, a city of about 70,000.

Chase said the roadside bombing, and another attack Monday in which six Marines were killed by small-arms fire, were still under investigation.

There is "no evidence whatsoever" that insurgents were tipped off by Iraqi forces in launching the attacks, he said. The explosion, which flipped the 30-ton lightly armored vehicle on its top, was caused by a stack of three anti-tank mines, the American Forces Press Service, a Defense Department organ, reported yesterday, citing an unnamed senior defense official.

During yesterday's operation, resistance was sporadic from insurgents wielding small arms and rocket-propelled grenades. No casualties were reported. Marines discovered a pair of buildings linked by trip wires and packed with 155mm artillery rounds scattered throughout.

Mines reportedly coming from Iran

NEW YORK — Some sophisticated new roadside bombs being used against U.S. and Iraqi troops are being designed in Iran and shipped from there, The New York Times reported in today's editions.

Citing U.S. military and intelligence officials, the Times said the information about the origin of the new weapons suggests a new level of cooperation between Iranian Shiite Muslims and Iraqi Sunnis against the U.S. presence in Iraq. According to military bomb experts, the new weapons are designed specifically to target armored vehicles. They first began appearing about two months ago.

Some shipments may have been brought over the Iranian border by Hezbollah or Iran's Revolutionary Guard, Pentagon and intelligence officials said.

Reuters