Car bombings shook the streets leading to Baghdad's most revered Shiite Muslim shrine Wednesday, and police reported at least seven people were killed and 27 others wounded.

The simultaneous blasts at two key intersections in the Kazimiyah district were the latest blows in an unending series of apparent attacks by Sunni extremists bent on terrorizing Iraq's Shiite majority and inflaming hostilities between the two sects.

Northeast of Baghdad, in several sections of the violence-wracked city of Baqouba, Iraqi troops and U.S. helicopter gunships were reported attacking Sunni militants of the group Al Qaeda in Iraq. A medical official said the bodies of eight gunmen were brought to the hospital. The U.S. military said it was looking into the report.

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Elsewhere, assassins killed a police official and an aide to Iraq's pre-eminent Shiite cleric.

The new bloodshed came a day after followers of anti-American Shiite cleric Muqtada al-Sadr pushed through a resolution in parliament requiring the Baghdad government to obtain legislative approval for future extensions of the U.N. mandate for U.S.-led forces in Iraq.

The current mandate doesn't expire until Dec. 31, but Tuesday's action added to the debate — in Baghdad and Washington — over whether and when U.S. troops should be pulled out.

U.S. Ambassador Ryan Crocker contended that things "could get very much worse" without the U.S. presence.

"I don't see an endgame, as it were, in sight," Crocker said in an interview broadcast Wednesday on NPR. "And that is why I get a little bit concerned when Americans talk about, well, we have got a couple of more months, and then we have to make final decisions."

The last of five brigades scheduled to reinforce U.S. troops in Baghdad and its surroundings will arrive in the "next couple of weeks," but it may take up to 60 days for it to fully establish itself, Brig. Gen. Kevin J. Bergner, a U.S. command spokesman, told reporters.

The brigades are the key element of a "surge" of 30,000 U.S. troops that began arriving in February to try to restore order to central Iraq.

In one of Wednesday's bombings, a parked car exploded at al-Zahraa Square, an intersection a half-mile from the large, golden-domed Kazimiyah shrine, in an area of closely packed homes and shops that is largely controlled by al-Sadr's Mahdi Army militia.

Hussein Alwan, 50, a bakery shop owner, said there were no police or troops nearby to be targeted, "just civilians."

"We rushed over and saw people dead or injured in burning cars, and we tried to save them while waiting for the firemen and ambulances," he said.

The second explosion, also of an unoccupied vehicle, occurred at the Aden intersection, at the western entrance to the Kazimiyah quarter. Police, meanwhile, found and disabled a third car bomb on a Kazimiyah street, said an officer at the Interior Ministry, speaking on condition of anonymity because he was not authorized to release the information.

Police initially put the death toll at five, but raised it to seven as the morning wore on.

The clashes in Baqouba, the Diyala province capital 35 miles north of Baghdad, erupted a day after the Iraqi army formally opened a new operations center there "to liberate Diyala from Al Qaeda elements."

That meeting Tuesday was punctuated by blasts from four mortar rounds landing outside, apparently fired by those Al Qaeda "elements."

On Wednesday, Iraqi and U.S. troops were deployed along the city's main streets as U.S. helicopter gunships fired on what were described as Al Qaeda strongholds in four Baqouba districts, police said. At Baqouba hospital, a medical source said the bodies of eight unidentified gunmen had been brought in.

The police and medical sources spoke on condition of anonymity, out of concern for their personal security.

In southern Iraq, three gunmen in a speeding automobile shot and killed a junior aide to the country's pre-eminent Shiite Muslim cleric, Grand Ayatollah Ali al-Sistani, police and a member of the ayatollah's office.

Complete coverage is available in FOXNews.com's Iraq Center.

Sheik Raheem al-Hasnawi, al-Sistani's representative in the al-Mishkhab area, 20 miles south of the southern Shiite shrine city of Najaf, was killed around 11 p.m. Tuesday near his home on the north side of Najaf, said the officials, who spoke on condition of anonymity out of security concerns.

Further details were not immediately available. Both intra-Shiite violence and attacks by Sunni extremists have claimed the lives of Shiite figures in Iraq's sectarian-political turmoil.

Police Maj. Enad Khattab was shot and killed along with his brother about 10 p.m. Tuesday as they drove in central Beiji about 155 miles north of Baghdad, a local police officer reported. He spoke on condition of anonymity out of security concerns.

At Wednesday's news briefing, Bergner offered no news about five Britons kidnapped May 29 from Iraq's Finance Ministry.

"We are receiving information from both the Iraqi people and Iraqi security forces and are taking all necessary actions that can be taken to pursue their safe release," he said. The Shiite Mahdi Army militia is widely suspected of having abducted the men.