The raids, dubbed "Operation Arrowhead Ripper," took place in Baqouba, the capital of Diyala province, and involved air assaults under the cover of darkness, the military said in a statement. The operation was still in its opening stages, it said.
Ten thousand U.S. soldiers were accompanied by attack helicopters, Strykers and Bradley Fighting Vehicles, the statement said.
The operation was part of new U.S. and Iraqi attacks on Baghdad's northern and southern flanks, aimed at clearing out Sunni insurgents, Al Qaeda fighters and Shiite militiamen who had fled the capital and Anbar during a four-month-old security operation, military officials said.
A top U.S. military official said Monday that American forces were taking advantage of the arrival of the final brigade of 30,000 additional U.S. troops to open the concerted attacks.
"We are going into the areas that have been sanctuaries of Al Qaeda and other extremists to take them on and weed them out, to help get the areas clear and to really take on Al Qaeda," the senior official said on condition of anonymity because he was not authorized to speak about the operation. "Those are areas in the belts around Baghdad, some parts in Anbar province and specifically Diyala province."
Al Qaeda has proven to be an extremely agile foe for U.S. and Iraqi forces, as shown by its ability to transfer major operations to Baqouba from Anbar province, the sprawling desert region in western Iraq. There is no guarantee that driving the organization out of current sanctuaries would prevent it from migrating to other regions to continue the fight.
In recent months, the verdant orange and palm groves of Diyala have become one of the most fiercely contested regions in Iraq. The province is a tangle of Shiite and Sunni villages that has played into the hands of Al Qaeda and allied militants who have melted into the tense region and sought to inflame existing sectarian troubles.
Al Qaeda has conducted public executions in the Baqouba main square and otherwise sought to enforce an extreme Taliban-style Islamic code. The terror organization's actions in the province have caused some Sunni militants, Al Qaeda's natural allies, to turn their guns on the group with American assistance and blessing. Some militant Shiites are likewise joining government forces in a bid to oust the foreign fighters and Muslim extremists.
The death toll in sectarian violence Monday skyrocketed after a brief period of relative peace. At least 111 people were killed or found dead nationwide, with 33 bodies of torture victims showing up in Baghdad alone.
Well to the south, Iraqi officials reported as many as 36 people were killed in fierce overnight fighting that began as British and Iraqi forces conducted house-to-house searches in Amarah, a stronghold of the Shiite Mahdi Army militia.
The U.S. military issued a statement that said at least 20 people were killed in clashes with coalition forces. A spokeswoman for Britain's Ministry of Defense said British soldiers played a supporting role to Iraqi security forces during the raid and fighting in Amarah. She spoke on condition of anonymity, which is ministry policy.
On Tuesday, police said clashes between Mahdi Army fighters and Iraqi security forces continued into a second day in another southern Iraqi city, Nasiriyah, about 320 kilometers (200 miles) southeast of Baghdad.
Eight people were killed there a day earlier, and more than 60 injured, mostly policemen, authorities said.
Nine mortar shells were launched early Tuesday at Iraqi police headquarters in the town, and three policemen were injured, a police officer there said on condition of anonymity out of security concerns. A vehicle was also destroyed in the shelling, he said.
Two civilians were wounded in another round of shelling in a residential area nearby, the officer said.
A curfew was imposed on Nasiriyah on Monday, and remained in effect a day later.
The operations on Baghdad's flanks were opened by the U.S. 3rd Infantry Division, which has taken over dangerous Al Qaeda-infested regions to the south. The division began its drive into the Salman Pak and Arab Jabour districts on the city's southeastern fringe over the weekend.
At the time, ground forces commander Lt. Gen. Raymond Odierno said U.S. troops were heading into those areas in force for the first time in three years.
The military said in a statement Monday that fighter jets dropped "four precision-guided bombs" in support of 1,200 U.S. soldiers from the 3rd Infantry as they started moving on Al Qaeda targets.
Multi-National Division-Baghdad, which has run the security operation in the capital since it began on Feb. 14, has increased pressure on districts to the northwest of the city to cut supply and reinforcement lines from Ramadi, the capital of Anbar province, to the Baqouba region.
"We're focusing up in the northwest to apply force in an area that's been important to Al Qaeda and its associates as they move between Ramadi and Baqouba. That work, together with the developing efforts to provide local security through the (Sunni) tribes in Abu Ghraib and Amariyah, is putting pressure on Al Qaeda," said Lt. Col. Scott Bleichwehl, division spokesman.
Some Sunni tribes, which had fought with or offered sanctuary to Al Qaeda in Anbar province, have risen up against the group and are now receiving arms and training from U.S. forces. American military officials are trying to spread that success to Al Qaeda areas now under attack.
Prime Minister Nouri al-Maliki, a Shiite, told visiting U.S. Defense Secretary Robert Gates last week that the United States should stop arming Sunnis who may have been part of the insurgency, according to officials in his office. The officials spoke on condition of anonymity because they were not authorized to release the information. Al-Maliki repeated that position in a television interview in Baghdad on Monday.