A homicide truck bomber struck an Iraqi police agency in northern Iraq on Sunday, killing at least seven people and wounding 50, police said, while overnight clashes between U.S. troops and Shiite militiamen reportedly left at least five people dead and 19 wounded.

The explosion, which occurred about 10:30 a.m., devastated a building housing the local highway police headquarters in the Albu Ajil village on the eastern outskirts of Tikrit, a police officer said, speaking on condition of anonymity because of security concerns.

The attacker detonated his payload after smashing into a blast wall, flattening a small reception building and causing heavy damage to the main two-story building just 20 yards away, the officer said, adding that most of the seven killed and 50 wounded were police.

Police and rescuers dug through the rubble in a desperate search for survivors or bodies of more victims. About 60 vehicles inside the compound also were destroyed.

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"It was a huge blast, my house was damaged," said Khalaf Eidan, a 45-year-old shopkeeper who lives nearby. "I thank God that none of my children were hurt."

Tikrit, 80 miles north of Baghdad, was ousted leader Saddam Hussein's hometown.

The blast was the deadliest of a series of attacks and other violence that killed at least 22 people, many targeting Iraqi police as militants continue to hammer the country's shaky security forces. The terror campaign against Iraqi troops and police appears designed to blunt U.S. progress in creating a stable local force so the Americans can go home.

In Baghdad, police and witnesses in Baghdad said overnight clashes between U.S. troops and Shiite militiamen left at least five people dead and 19 wounded in an eastern district. The U.S. military said it was looking into the reports.

The fighting in the predominantly Shiite Fidhiliyah area on the Baghdad's outskirts broke out after a U.S. military convoy came under attack near the local offices of Muqtada al-Sadr, the anti-American cleric whose Mahdi Army militia has recently stepped up attacks on American troops, according to police officers in the area who declined to be identified because they weren't authorized to release the information.

AP Television News video footage shot Sunday showed the charred skeleton of what appeared to be a Humvee and a low-flying Apache helicopter firing flares as several hundred people, including teenagers and children, were gathered around the smoldering vehicle below, mostly teenagers and children.

The police and witnesses said those killed and wounded were Iraqis and included bystanders caught in the crossfire.

U.S. troops stormed al-Sadr offices and detained 16 men, according to police and an official in al-Sadr's office who spoke anonymously because he feared retribution.

Al-Sadr's Mahdi Army militia fought U.S. forces for much of 2004. More recently, the U.S. military has repeatedly blamed the militia for the death of American soldiers in deadly roadside bombs it says are provided by Iran.

Al-Sadr himself resurfaced in late May for the first time in nearly four months, ending what U.S. officials have said was his voluntary exile in neighboring Iran, apparently to avoid arrest.

His public comments — in a Friday sermon May 25 and a television interview last week — have since been heavily anti-American, calling for the withdrawal of all foreign troops from Iraq and blaming the Americans for all of Iraq's woes.

In other violence Sunday, a roadside bomb struck a police patrol near a gas station in Balad Ruz, 45 miles northeast of Baghdad, killing one policeman and wounding 6 other people — five officers and one civilian, according to the provincial police center for Diyala, a hotbed of the Sunni insurgency that has become increasingly dangerous since the beginning of the Baghdad security operation nearly four months ago.

Militants have fled the capital to avoid capture and forced the U.S. military to dispatch about 3,000 more American forces to Diyala from already overtaxed reinforcements arriving in Baghdad.

A homicide car bomber smashed into a police patrol about 12 miles south of the provincial capital of Baqouba, killing two policemen and wounding three others, officers at the provincial police center said, speaking on condition of anonymity because they weren't authorized to release the information.

Gunmen elsewhere in the volatile province killed two policemen and a civilian in two separate attacks in the Shiite enclave of Khalis, they said.

Violence also struck civilians as a homicide car bomber exploded in a line of cars waiting for gas about 11:45 a.m. in Baiyaa, an area in western Baghdad that has seen a recent rise in sectarian violence despite a U.S.-Iraqi security crackdown that began on Feb. 14.

About 15 minutes later, parked car bomb also ripped through cars waiting for gas in the predominantly Sunni neighborhood of Sadiyah in southwestern Baghdad.

In northern Iraq, a roadside bomb targeted a convoy of a Kurdish brigade that had recently been deployed in western Baghdad as part of the security operation, killing one soldier and wounding three, an army officer from the brigade said on condition of anonymity.

The attack occurred in Sulaiman Pak, 90 miles south of the oil-rich city of Kirkuk.

In another developments, the Iraqi high tribunal said it will issue a verdict on June 24 in the trial of Saddam's cousin known as "Chemical Ali" and four other former regime officials who face a possible death sentence if convicted of war crimes and crimes against humanity for their roles in a 1980s military campaign against the Kurds.

Jaafar al-Moussawi told The Associated Press the five defendants were told of the decision Sunday in a short court session.

Saddam's cousin Ali Hassan al-Majid and the other defendants face charges that include crimes against humanity for their roles in the 1980s military campaign code-named Operation Anfal. If convicted, they could be sentenced to death by hanging.

Saddam was a defendant in the case but was hanged last year after his conviction for the killing of 148 Shiite Muslims in Dujail after a 1982 attempt on his life.

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