Iraqi and US forces formally began the second phase of an ongoing security plan, Operation Together Forward.
The operation is aimed at pacifying a capital that has seen thousands killed in insurgent and Shiite-Sunni violence in recent months.
As part of the plan, officials brought in an extra 6,000 Iraqi police, along with 5,500 American soldiers pulled in from missions elsewhere in Iraq.
The first phase began in June with more than 50,000 Iraqi and US troops but failed to curb the violence that has seen daily bombings, shootings and sectarian killings leave scores dead in the streets of the capital.
A recent United Nations report said about 6,000 people had been killed in May and June across Iraq, most of them in Baghdad.
Security crackdown
Insurgents have defied the security crackdown, carrying out deadly attacks on mosques and markets, while rival Shiite and Sunni death squads have rampaged through the capital's neighbourhoods kidnapping, torturing and killing.
"We must dramatically reduce the level of violence in Baghdad that is fuelling sectarianism," said Major General James Thurman, commander of US-led forces in the Baghdad region.
"Iraqi and US forces will help the citizens of Baghdad by reducing the violence that has plagued this city since the Samarra bombing," he said.
Maj Gen Thurman was referring to an insurgent attack on a revered Shiite mosque in February that triggered tit-for-tat Shiite-Sunni reprisals.
Under the first phase of Together Forward, troops killed or captured 411 "murderers associated with death squads", a US statement said, using the military's new catch-all term for illegal armed groups.
Blackhawk down
US-led coalition forces spokesman Major General William Caldwell said a team of divers was searching for two US servicemen missing after their Blackhawk helicopter crashed into water in restive Anbar province on Tuesday.
"The helicopter went down with some kind of technical difficulty. It crashed in water. Dive teams have gone in today," Caldwell told reporters.
The chopper crash was the third since May. The previous two were allegedly shot down by groups linked to the Al-Qaeda militant network.
The 130,000-strong US force in Iraq relies extensively on helicopters to transport troops and supplies, survey territory and carry out air strikes on insurgent forces.
Many of the roads around Iraq are not regarded as safe for ground convoys because of the risk of roadside bombs and ambushes -- the biggest cause of casualties for the military since the 2003 invasion.
Kidnap suspects arrested
Meanwhile four Iraqis have been arrested for their alleged involvement in the abduction of Crhsitian Science monitor journalist Jill Carroll.
She was seized in January while on her way to meet a Sunni Arab politician in Baghdad.
US troops also raided three houses where she was believed to have been held captive before her release, which was made possible by the intervention of several leading Sunni leaders.
The four captives included a member of the Mujahedeen al-Shura, an umbrella body of Sunni insurgent groups which is led by Al-Qaeda.
The suspects were picked up in a series of raids in western Iraq, starting with a house in Habbaniyah, 13 kilometres west of Fallujah in Anbar province, which had been spotted by a young US military officer.
Details of the decor, including a bookshelf in an upstairs bedroom of the two-storey, stone-built detached house, matched descriptions of a place where Ms Carroll had been held during her three-month ordeal.