In the deadliest attack, in the northern city of Irbil, a suicide car bomber wearing a police uniform killed at least 15 traffic policemen and wounded 100 others during morning roll call at a police headquarters, authorities said.

Separately, the U.S. military said a soldier was killed by a roadside bomb in northwest Iraq, increasing to at least 48 the number of American troops killed by hostile fire this month.

Yesterday's attacks - including mortars and heavy machine-gun fire - underscored the apparent strategy of the insurgents: As U.S. and Iraqi commanders hit hard in one region, they hit back in another.

Two operations by U.S. Marines and the Iraqi army in restive Anbar province do not appear to have seriously undermined the ability of insurgents to move forces and launch attacks.

On Thursday, U.S. Air Force F-16 fighter jets dropped 500-pound bombs near two small towns on the Syrian border in western Anbar, and over the weekend 2,000 Marines and Iraqi troops launched two separate offensives aimed at killing and capturing rebels in the province.

Insurgent-led violence fell off after Thursday's attack. Then Sunday, a man wearing an explosives vest walked into a kabob restaurant in central Baghdad and killed at least 23 people, including seven police officers. Yesterday, deadly attacks in Irbil and Baghdad followed.

Early yesterday morning, insurgents attacked a police station in southern Baghdad with rocket-propelled grenades, mortars and heavy machine-gun fire before detonating a car bomb, according to the Iraqi Interior Ministry. When police started to venture out after the first blast, a second car bomb exploded.

Insurgents and police battled at a nearby intersection. At another intersection, insurgents wearing Iraqi army uniforms set up roadblocks and roadside bombs to deter reinforcements, Iraqi officials said.

While Iraqi officials said their troops defeated the insurgents without help from U.S. forces, residents said the insurgents appeared to have had the upper hand until American troops and attack helicopters arrived.

The U.S. Army's Third Infantry Division said in a statement that the American military task force in Baghdad fended off the attack. At least eight police officers and a baby were killed and at least 23 were wounded in the fighting, police said.

A subsequent statement from the U.S. military said that 10 insurgents were killed and 20 were captured.

Later yesterday, a suicide car bomber hit an Iraqi army brigade headquarters in Tikrit, north of Baghdad, killing five and wounding nine, authorities said.

As long as U.S. and Iraq military forces continue to wage offensives in areas populated by the nation's minority Sunni Muslim population - the base of the insurgency - the violence will continue, said Tariq Hashimi, the secretary-general of the Iraqi Islamic Party, a major Sunni political group.

Hashimi said that for the insurgency to end, American and Iraqi officials have to negotiate with Sunni groups to bring more Sunnis into the political process.

On Sunday, Sunni Muslims submitted a list of 15 candidates for a Shiite-dominated committee drafting Iraq's constitution, but they were having second thoughts yesterday about a demand made by legislators that the group be endorsed by representatives of the entire community. The snag could delay the constitutional process, further eroding the little time left for the charter to be drafted by mid-August.

Meanwhile, the U.S.-led offensive in Anbar province dubbed Operation Spear ended yesterday. It was launched last week with 1,000 Marines and Iraqi soldiers to ebb the flow of foreign fighters entering from Syria. The four-day campaign in the border city of Karabilah, 200 miles west of Baghdad, killed about 60 insurgents, the Marines said. One Marine died.

Osama Jadaan al-Dulaimi, the head sheikh for Karabilah, said that the death toll had been high and that it would turn moderate Sunnis into insurgents. He said 150 civilians were killed and 250 to 300 were wounded.

The Marines did not respond to requests for comment on Dulaimi's statements, which could not be independently confirmed.

Operation Spear ran in conjunction with Operation Dagger, a similar engagement north of Baghdad.

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