BAGHDAD, Iraq — Insurgents defied a much-touted military crackdown in the capital yesterday, targeting police checkpoints, the Oil Ministry and convoys of U.S. and Iraqi troops.

In at least five suicide bombings within six hours, insurgents killed 20 members of the fledgling security forces. By the end of the day, militants had killed at least eight other Iraqis, as the death toll in a monthlong escalation of violence pushed beyond 720.

In Hillah, about 60 miles south of Baghdad, two suicide bombers attacked a large crowd of police special forces today, killing at least 10 policemen and wounding 25, police and hospitals officials said.

Armored sport-utility vehicles and pickups carrying Iraqi police and national guardsmen sped through the capital yesterday, drawing fire and scattering civilian drivers trying to distance themselves from the targeted convoys. Small-arms fire from insurgent ambushes in several Baghdad neighborhoods crackled throughout the day as the embattled new government continued deploying what it said would be 40,000 police and troops.

Prime Minister Ibrahim al-Jaafari's spokesman, Laith Kubba, said more than 500 arrests had been made in the first two days of the sweep.

Iraqi and U.S. officials had predicted militants besieging Baghdad with daily suicide bombings and assassinations would flee the crackdown, announced Thursday.

Iraqi and U.S. officials had planned to erect 675 checkpoints along the capital's outskirts to prevent insurgents from fleeing, but they have yet to set up an effective cordon. Instead, insurgents staged attacks across the capital, targeting the very checkpoints meant to ensnare them.

Yesterday's deadliest attack occurred when about 50 insurgents stormed a checkpoint, killing nine Iraqi troops attempting to monitor and search passing vehicles. The government said 14 insurgents died in the exchange of gunfire.

Kubba said the government would press on, with street-by-street, house-to-house searches planned to flush out insurgents.

"Search operations and raids have allowed us to arrest 500 people and find arms caches in several houses," he said.

While Iraqi police and soldiers were scrambling to seal off the capital, some U.S. officials expressed concern that the crackdown would lack "precision" and further erode public support for al-Jaafari's government, which took power April 28 and has witnessed a concerted challenge to its authority from insurgents.

"One thing we've stressed with them is the need for precision," a senior U.S. military official said of the raids. "You can't just roll people up. It alienates them."

Iraqi and U.S. soldiers arrested a former general in Saddam Hussein's intelligence service who was also a member of his Fedayeen secret police during a raid in western Baghdad, the scene of some of yesterday's heaviest fighting.

"He now leads the military wings of several terror cells operating in the west Baghdad neighborhood of Ghazaliyah," the military said in its announcement about the former general. It did not release his name or provide further details.

As fighting raged in such western neighborhoods, Iraq's new legislators pounded out their first agreement on the 15 basic articles to guide their new constitution, including democracy, federalism and separation of powers and making Islam the state religion.

The 55-member parliamentary committee has until Aug. 15 to draft the constitution, which is subject to approval in an October referendum.

Troops belonging to the U.S.-led coalition are backing the raids, but officers have emphasized it is an Iraqi-led mission.

Shortly after dawn, a suicide attacker plowed a bomb-laden vehicle into a convoy of Iraqi special forces in the Madain neighborhood in south Baghdad, killing one policeman and a civilian.

Three hours later, a car bomb killed two Iraqi commandos in the same neighborhood.

Just before 1:30 p.m., a suicide bomber crashed into the outer security barriers at the Iraqi Oil Ministry, killing two guards and injuring six bystanders.

At 4 p.m., a car bomb killed three more Iraqi policemen in the volatile Adamiya neighborhood. In the Dora section, gunmen killed two police sergeants assigned to guard government officials. Near sunset, a suicide bomber hit an Iraqi patrol, killing two policemen.

A car bomb apparently aimed at a U.S. military convoy in the city of Tuz Khormatu, south of Kirkuk, killed two Iraqis.

Three bodies, two of them handcuffed, were found in Baghdad with evidence they had been killed execution-style. A police identification card was found near one of the bodies.

The U.S. military command announced that another campaign in western Iraq aimed at hobbling the insurgency had wrapped up after four days. Fourteen militants were killed and more than 30 arrested, the military said.

Two U.S. Marines died in the mission focused on Haditha, which the military says is a major crossroads for Islamic militants from other countries.

Information about today's bombing provided by The Associated Press.