U.S., Iraqi troops go after Samarra insurgents
Nearly three dozen children killed in Baghdad bombings
Car bomb detonates near base in western Baghdad.
U.S. forces strike safe house in Falluja linked to al-Zarqawi.
Two female Italian hostages freed after three weeks.
BAGHDAD, Iraq (CNN) -- U.S. and Iraqi forces moved into the Sunni Triangle city of Samarra late Thursday in one of the largest offensives in several months.
Earlier, explosions in Baghdad claimed more than 40 lives, most of them children.
A brigade-size force of U.S. and Iraqi national guard troops had reached the center of Samarra by early Friday morning, according to CNN correspondent Jane Arraf, embedded with a unit of the U.S. 1st Infantry Division.
Supported by tanks and aircraft, troops were going through the city sector by sector, clearing buildings and mosques. Electricity was being cut to some sections.
Gunfire, explosions and rocket-propelled grenades could be heard as Arraf reported from the scene.
U.S. military officials estimated that more than 2,000 Iraqi insurgents and 250 foreign fighters were in the city, which is 70 miles north of Baghdad.
A U.S. Army brigade typically has about 3,500 troops, although that number can vary.
After the transfer to Iraq sovereignty in June, the U.S. military agreed to stop patrolling Samarra. But insurgent attacks continued, and American forces returned three weeks ago.
Bloody day in Baghdad
Earlier Thursday, nearly three dozen children died and many more were wounded when car bombs exploded at a community celebration in Baghdad where U.S. soldiers were handing out candy.
The attacks at the festive opening of a sewage plant in Baghdad killed at least 41 people. Another car bomb had already killed a U.S. soldier and two Iraqi police officers.
An Islamist Web site with ties to the Unification and Jihad group posted a message it said is from the group's military wing claiming responsibility for three suicide attacks.
The message -- dated September 30 and posted shortly after 3 p.m. ET -- said "three knights from the Martyrs Brigades of the Tawhid and Jihad have performed three heroic attacks."
The message said the first attack "targeted the municipality of the city of Abu Ghraib west of the capital Baghdad, where its director and his band were meeting with their American masters. It resulted in the death of five U.S. soldiers and several Iraqi police."
The message added, "The other two knights have carried out an attack against a U.S. convoy and thank God the attack was successful."
The group is believed to be led by Abu Musab al-Zarqawi, and has also claimed responsibility for beheading two Americans last week -- Jack Hensley and Eugene "Jack" Armstrong.
Thursday's attacks added to what U.S. military officials said already was a record number of car bomb attacks in a month.
In a radio interview, Defense Secretary Donald Rumsfeld acknowledged the violence in Iraq is "getting worse" and he said he expects it to increase as Iraqi elections approach.
The government is about to launch an offensive to stamp out insurgents and terrorists, a senior Iraqi interim government official said.
Interim Iraqi Deputy Prime Minister Barham Saleh, speaking to reporters, said, "We are obviously seeing a major onslaught by the terrorists on Baghdad and some other Iraqi cities."
Interim Iraqi Prime Minister Ayad Allawi, in London, reiterated that despite the violence elections will be held in January for a transitional national assembly.
And the hostage-takings continue. The Arabic language television network Al-Jazeera reported the abduction of 10 more people in Iraq -- two Indonesian women, six Iraqis and two Lebanese. Two French journalists and a British engineer remained in captivity. (Full story)
The Baghdad car bombings overshadowed other developments.
A suicide attack hit a compound housing the al-Rissala police station in the Abu Ghraib neighborhood in western Baghdad, Iraqi police officials said.
The dead included a Task Force Baghdad soldier and two Iraqi police officers, Iraqi and U.S. officials said.
With the soldier's death, 1,056 U.S. military personnel have died in the Iraq war. Three other soldiers were wounded, the U.S. military said. The Ministry of Health said 60 more people were wounded.
Later, U.S. military officials said two car bombs detonated as Iraqi officials were conducting the sewage plant opening. Witnesses told CNN many children there were being offered candy by soldiers.
The witnesses told Iraqi police that gunmen in a four-wheel-drive vehicle started shooting at American forces and Iraqi National Guard members. Then two car bombs exploded.
Iraqi National Guard members twice tried to stop a car from driving into the area, then opened fire and the car exploded.
A half-mile away, another vehicle detonated at an Iraqi national guard checkpoint two miles west of Baghdad University, U.S. military officials said.
Among the wounded were 139 at Yarmouk Hospital, seven at Neurosurgical Hospital, seven at Kadhamiya Hospital, and five at Children's Hospital. There were five wounded people at Khark Hospital but it was unclear if they were part of the Yarmouk total.
Other developments:U.S. and Iraqi forces are gearing up for a major offensive to enforce stability in Falluja, Sadr City and other hot spots three months before elections, a senior Iraqi official said. Meanwhile, senior military officials said U.S. and Iraqi troops in the past month have killed or captured more than 100 al-Zarqawi associates and have killed six members of al-Zarqawi's inner circle.The British government said it was ready to listen to kidnappers holding hostage Ken Bigley in Iraq but was not prepared to negotiate or pay a ransom. (Full story) U.S. forces struck a suspected safe house in Falluja used by terrorists linked to al-Zarqawi, according to the coalition press office. Three people died and eight others were wounded in the air strike, an Iraqi hospital official said. Four children were among the wounded, a Falluja General Hospital official said.
CNN's Jane Arraf, Brent Sadler, Mike Mount, Ayman Mohyeldin, Ingrid Formanek, Faris Qasira, Mohammed Tawfeeq and Barbara Starr contributed to this report.