Suspected Sunni insurgents bombed and badly damaged a span over the main north-south highway leading from Baghdad on Tuesday — the third bridge attack in as many days in an apparent campaign against key transportation arteries.

The attack occurred 35 miles south of Baghdad and just six miles south of a bridge brought down on Sunday by what was believed to be a homicide truck bomber. Three U.S. soldiers guarding that bridge were killed in Sunday's blast.

The explosion at 7:30 a.m. Tuesday — not thought to be a suicide bomb — struck a bridge linking the villages of al-Qariya al-Asriyah and al-Rashayed in northern Babil province. No injuries were reported.

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About 60 percent of the bridge was damaged, and cars could still pass over it via one lane, police said. But debris from the blast fell on the main north-south expressway below, further complicating efforts to reopen that main artery, closed after Sunday's blast dropped masses of concrete onto the roadway.

On Monday, a parked truck bomb destroyed a bridge carrying traffic over the Diyala River in Baqouba, 35 miles northeast of Baghdad. There were no casualties, but vehicles were being forced to detour to a road running through Al Qaeda-controlled territory to reach important nearby cities.

Baqouba is the capital of Diyala province, which is swarming with Al Qaeda fighters. Those militants were driven out of Baghdad by the four-month-old U.S. security operation and out of Anbar province west of the capital by Sunni tribesman who rose up against the terrorist group.

Fierce clashes broke out between joint U.S.-Iraqi forces and Al Qaeda militants in the city Tuesday morning, leaving two Iraqi soldiers and six militants dead, police and hospital officials said, speaking on condition of anonymity because of security concerns. The fighting also prevented university students at nearby colleges from taking their final exams, according to the provincial police center.

Elsewhere in the province, gunmen stormed the house of the Sunni mayor of Muqdadiyah, about 60 miles north of Baghdad, forcing the family members outside, then blowing up the house, the police officials said. Najim al-Harbi, a member of the Iraq Islamic Party, was not home when the attack took place.

The attacks on the bridges were only the latest in a bid to deepen turmoil in Iraq, especially on the vital transportation network linking Baghdad to the rest of the country. Such bombings — especially suicide attacks — are an Al Qaeda trademark and one of the group's many and ever-shifting tactics against U.S. and Iraqi forces.

Earlier this month, a bomb heavily damaged the Sarhat Bridge, a key crossing 90 miles north of the capital on a major road connecting Baghdad with Irbil, Sulaimaniya and other Kurdish cities.

In March and April, three of Baghdad's 13 bridges over the Tigris River were bombed. The attacks were blamed on Sunni insurgent or Al Qaeda attempts to divide the city's predominantly Shiite east bank from the mostly Sunni western side of the river.

The most serious attack, an April 12 suicide truck bombing, collapsed the landmark Sarafiyah bridge and sent cars plunging into the brown waters of the Tigris. Eleven people were killed.

Paul Kane, a fellow with the International Security Program at Harvard University's Kennedy School of Government, said the attacks on bridges are an extension of earlier insurgent attacks on "electric generation sites, infrastructure for water and also the obvious target of oil pipelines."

Kane noted that Iraq does not have railroad service so insurgents "may be at the end of the transit list. If anything, it means they're trying to be creative and they're running out of targets."

Tumult also arose in Iraq's fragile political structure Monday when lawmakers declared themselves fed up with the parliament speaker and voted to oust the controversial Sunni politician from his powerful post.

Mahmoud al-Mashhadani is a physician who was jailed by Saddam Hussein and who had said from the parliament speaker's chair that those who attack American forces should be treated as heroes. He was voted out in a closed session of the Shiite-dominated 275-member legislature.

His ouster appeared to have grown out of a shouting match Sunday with lawmaker Firyad Mohammed Omar, a Shiite Turkoman.

Omar had complained to the speaker about the heavy-handedness of al-Mashhadani's bodyguards; al-Mashhadani responded abusively, according to lawmakers who spoke on condition of anonymity because of the sensitivity of the issue. Omar told fellow legislators that the speaker's guards had assaulted him.

Al-Mashhadani's deputy, Khaled al-Attiyah, who chaired the closed session, will assume the duties of the speaker until a replacement is chosen.

"It's an illegal decision made by a juvenile house," al-Mashhadani told the U.S.-funded Radio Sawa in an interview posted on the Internet.

Al-Mashhadani is part of the Accordance Front, parliament's largest Sunni Arab bloc with 44 of the house's 275 seats. Salim Abdullah, a fellow lawmaker from the Accordance Front, said it would offer a replacement for al-Mashhadani within a week.

The speaker's job is allotted to a Sunni member of parliament according to an agreement among lawmakers who struggled for months to chose their leadership, a prime minister and government.

"We agreed to replace him because we want to improve the house's performance," Abdullah told The Associated Press.

But al-Mashhadani told Radio Sawa that if his performance as speaker were below par, Shiite Prime Minister Nouri al-Maliki's was "much worse." The level of competence of President Jalal Talabani, a Sunni Kurd, was "even worse because he does nothing," the former speaker said.

The Al Qaeda front group Islamic State in Iraq, meanwhile, posted a video showing what it said were 14 captive members of the Iraqi security forces and threatening to kill them in 72 hours if their demands were not met, including the release of all female prisoners in Iraqi prisons. The hostages were shown in uniform standing in three rows; one of them repeatedly sighed and looked up at the ceiling. It wasn't clear when they were seized.

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