Meanwhile, an influential Sunni clerical group called Wednesday for the release of five Westerners taken hostage last week in a wave of kidnappings.
About 1,500 U.S. Marines from the 13th Marine Expeditionary Unit, 500 U.S. soldiers and 500 Iraqi soldiers were taking part in Operation Iron Hammer near Hit, 85 miles west of Baghdad, a U.S. Marine statement said. The forces would concentrate efforts in the Hai Al Becker region, where U.S. and Iraqi troops rarely patrol, it added.
"The Hai Al Becker region is suspected to be an al Qaeda in Iraq safe area and base of operations for the manufacture of vehicle car bombs, roadside bombs," the military said.
It added that the area is believed to be a stopping point for insurgents traveling down the Euphrates River from Syria into Iraq.
In other developments:
Also Wednesday, CBS News correspondent Cami McCormick (audio) reports Iraqi troops raised their flag at a base in Husaybah, near the Iraq border with Syria, to show they are reassuming control. The town was once a safe haven for insurgents before Operation Steel Curtain.
"And what this ceremony commemorates is the restoration of Iraqi control to that Syrian border around Husaybah, and all the way, frankly, from the northern border with Turkey down to Jordan," said General George Casey, the commander of U.S. troops in Iraq.
Iraqi forces are great when it comes to looking for a fight, but not so great in planning it. That's what CBS News correspondent Kimberly Dozier says reporters always hear from the Americans. "Today was a case in point," Dozier said. "We went out with the Iraqi highway patrol, looking for roadside bombs. The Iraqis brought their guns, but no food or water for a three-hour drive. As usual, the Americans had to provide.
"Iraqi forces are better supplied than in the past, but there are still major gaps. One American soldier says every time he goes out on a joint patrol, the Iraqi cops complain that their superior officers are stealing the money intended for supplies. None of the guys have wet weather gear for Iraq's torrential winter rains, only some of them have bullet-proof vests, and one policeman showed the Americans that he had only a single bullet to fire, in case anyone attacked," Dozier said.
In separate statements, the Association of Muslim Scholars, believed to have contacts with some Sunni insurgent groups, said the five Western hostages should be released as a humanitarian gesture. The association has helped mediate the releases of other Westerners taken captive in Iraq.
The five include four Christian aid workers — two Canadians, a Briton and an American — and German archaeologist Susanne Osthoff.
The association said releasing Osthoff would recognize Germany's "positive" stand toward Iraq. Germany strongly opposed the U.S.-led invasion in 2003.
The statement also noted that Osthoff is married to an Iraqi Muslim, "who is a member of the Shammar tribe from Mosul and she works as an archaeologist."
The Shammar tribe is one of the largest in Iraq and includes Shiites as well as Sunni clans. Vice President Ghazi al-Yawer is a senior figure in the tribe.
Osthoff and her Iraqi driver were seized Friday, and they later were pictured in a videotape blindfolded on a floor, with militants standing beside them. One of the militants was armed with a rocket-propelled grenade.
Kidnappers threatened to kill Osthoff and her driver unless Germany halted all contacts with the Iraqi government.
The four Christian aid workers were taken captive Saturday and appeared in a video broadcast Tuesday by Al-Jazeera television. A previously unknown group calling itself the Swords of Righteousness Brigade claimed they were spies working under the cover of Christian peace activists.
The association said their release would recognize their "good efforts in helping those in need."
Christian Peacemaker Teams said it was saddened by the videotape of their workers, who the statement said were working against the occupation of Iraq.
"We are angry because what has happened to our teammates is the result of the actions of the U.S. and U.K. government due to the illegal attack on Iraq and the continuing occupation and oppression of its people," the group said.
"They are four men who came to Iraq to work for peace and to explain their opposition to the occupation. They are not spies," Doug Pritchard, a Canadian co-director for Christian Peacemaker Teams, told CBC-TV.
"All of the Iraqi organizations and individuals who know us know that too, and we've encouraged them to speak out and they are doing that."
The latest attacks are part of a new wave of kidnappings police fear is aimed at disrupting the Dec. 15 parliamentary elections. U.S. and Iraqi officials hope a big turnout in the election will undermine the insurgency and improve chances for the United States and its partners to begin reducing troop levels in Iraq next year.