Iraqi military officials expressed hope Sunday that security gains from a yearlong crackdown against extremists will allow the removal of thousands of concrete barriers in six months that protect Baghdad residents from bomb attacks.

Meanwhile, Prime Minister Nouri al-Maliki spent the weekend touting the successes of the security operation that began one year ago and peaked last summer with the influx of thousands of U.S. troops. The operation helped restore some security to a country that in January 2007 was on the brink of civil war.

The U.S. military said Sunday that insurgent attacks had declined by 60 percent over the past year, but cautioned the war was not yet won.

"They are reminders that although the enemies of the people of Iraq are weakened, they can still recruit and conduct spectacular attacks," said Rear Adm. Gregory Smith, a U.S. spokesman in Baghdad.

Brig. Gen. Qassim al-Moussawi, the chief Iraqi military spokesman for Baghdad, said the government hoped within six months to reopen the Imams bridge, which spans the Tigris river and links a major Sunni neighborhood with a large Shiite district. The Imams was sealed and barricaded after nearly 1,000 Shiites, fleeing what they thought was a Sunni suicide bomber, died in a stampede on the bridge in 2005.

Al-Moussawi added that the government also would lift "all concrete walls from Baghdad streets," a promise that will be much harder to keep. The so-called Green Zone that houses the Iraqi government, parliament, and many of its officials is surrounded by thousands of concrete "blast walls" that enclose a huge portion of central Baghdad.

Several concrete walls and barriers also have been erected to dampen sectarian violence by separating or dividing Sunni and Shiite neighborhoods. There has never been a count of the barriers, but they are thought to number in the tens of thousands.

On Saturday, during a walking tour of Mansour — a predominantly Sunni neighborhood abutting the Green Zone — al-Maliki pledged that "we will break the concrete walls among Baghdad's neighborhoods this year, which we had put up temporarily."

Parts of Mansour, located in central Baghdad, were a stronghold of Al Qaeda in Iraq for much of the time following the U.S. invasion in 2003. It was cleaned up during the operation.

Al-Maliki has sought to benefit from the success of the yearlong crackdown against Al Qaeda in Iraq and rogue elements of radical Shiite cleric Muqtada al-Sadr's Mahdi Army. Besides the inflow of U.S. forces, much of that success also was due to a U.S. program that effectively hired many Sunni tribesmen and neighborhood fighters who once fought for Al Qaeda, and a cease-fire declared by al-Sadr last August.

On Sunday, a female suicide bomber struck a Shiite neighborhood, detonating after soldiers fired three bullets at her.

Casualty figures were disputed. Two doctors and a police officer, who spoke on condition of anonymity because they weren't authorized to release the information, said four people were killed and 12 wounded. The U.S. military, however, said the only death in the explosion was the bomber, although two Iraqi army soldiers were wounded.

According to the military, the bomber appeared to be a beggar with something bulky around her waist. When Iraqi troops asked her to raise her hands, she only lifted one and wires were seen in her other hand. After being shot at, she staggered to a nearby shop and blew up.

It was unclear what triggered the blast.

Female suicide bombers have been involved in at least 18 attacks or attempted attacks since the war began, including the grisly bombings of two pet markets that killed nearly 100 people on Feb. 1. Iraqi and U.S. officials have said the women used in the pet market attacks were mentally disabled and apparently unwitting bombers.

The military also said two U.S. soldiers were killed Sunday by small-arms fire in the volatile Diyala province, northeast of Baghdad, where troops are trying push out insurgents. The deaths raised to at least 3,963 members of the U.S. military who have died since the Iraq war started in March 2003, according to an Associated Press count.

U.S. forces killed four extremists and detained about three dozen suspects in operations around Iraq Saturday and Sunday, the military said in separate announcements.

Separately, a car bombing Sunday morning in the northwestern city of Mosul killed a police officer and two civilians, police there said. The U.S. military has said Iraq's third-largest city is the last major urban stronghold of al-Qaida in Iraq.