A pair of car bombs exploded in separate incidents Wednesday, with one killing six people and the other injuring six people, including four U.S. soldiers. Three U.S. soldiers were killed in separate incidents around the country.

In northern Iraq, a U.S. Army soldier was killed when he stepped out of his vehicle to investigate a roadside bomb and it exploded, a military spokesman said. A second American soldier died of his wounds following an attack on a patrol in the northern town of Mosul, U.S. command said in a statement. A third soldier was killed when a car bomb exploded near a traffic control point in Baghdad, a military statement said. Four other soldiers were wounded in the blast.

Also, Sheik Abu Anas al-Shami, 35, the spiritual leader of Abu Musad al-Zarqawi's (search) Tawhid and Jihad terrorist group, was killed in a U.S. airstrike several days ago in a Baghdad suburb, the man's father said. The U.S. military had no comment.

U.S. and Iraqi troops also battled with insurgents in the central city of Samarra, where U.S. forces had earlier claimed success against militants waging a 17-month insurgency, police said. At least one child was killed and five people wounded in the fighting, police said.

In Baghdad, U.S. aircraft and tanks continued their assault on Shiite militia positions in fierce fighting early Wednesday in the Sadr City slum, killing 10 people and injuring 92 others, hospital officials said.

The fighting came as U.S. and Iraqi forces searched for weapons caches and targeted "pockets of insurgents and terrorists" in the Shiite stronghold, an east Baghdad slum, the military said in a statement.

"The intent is to provide security for the people of Thawra so we can get back to the business of reconstruction," said 1st Cavalry Division commanding general Maj. Gen. Peter Chiarelli in a written statement. Thawra is an old name for Sadr City.

Two Car Bombs Hit Baghdad

In the first blast, a homicide attacker detonated a car bomb outside a photocopy shop in western Baghdad where Iraqi National Guard (search) applicants were readying their papers before heading to a nearby recruiting center.

At least six people were killed and 54 wounded, said Dr. Mohammed Salaheddin of the nearby Yarmouk Hospital (search).

Bloodied bodies, shattered glass and debris littered the street in the commercial neighborhood of Al-Jamiyah.

At least 13 vehicles were wrecked and the engine of the car was hurled some 150 feet away.

"A man in a black Opel car drove up near the shop and detonated the explosives," said policeman Ahmed Jassem.

Iraqi police and U.S. troops immediately cordoned off the area.

Interior Ministry official Col. Adnan Abdul-Rahman said the blast was caused by a homicide car bomber.

Insurgents have repeatedly targeted Iraqi police and national guard forces with bombings, mortar attacks and shootings in a bid to sow instability and disrupt U.S.-backed efforts to build a strong Iraqi security force. Hundreds have died in the attacks.

In the second car bomb, the explosion went off near a U.S. military convoy in Baghdad's Mansour district. The military confirmed the blast injured 4 U.S. soldiers and 2 local nationals.

The location of the blast was the same neighborhood where two Americans and a Briton were seized last week. Officials have confirmed that one of the Americans was killed and are investigating whether the second American suffered the same fate.

U.S. Strikes Sadr City

An Associated Press reporter near the scene of the strike in Sadr City said a U.S. C-130 gunship raked one area with heavy fire after rebels loyal to radical Shiite cleric Muqtada al-Sadr (search) opened fire with rocket-propelled grenades.

U.S warplanes and Apache helicopter gunships also carried out strikes. One helicopter was hit by groundfire but managed to return to its base, and one tank was disabled by a roadside bomb. There were no immediate reports of any injuries to U.S. forces.

Ten people died and 92 were injured, said Qassim Saddam of Imam Ali Hospital in Sadr City.

At one point, U.S. troops took to the slum rooftops to chase down five rebels armed with assault rifles.

Later in the day, soldiers occupied the Jolan Club, a large enclosed sports complex with soccer fields and basketball courts that the Americans believed was being used to store weapons. No arms were found, however.

Large swathes of Sadr City were nearly deserted by late morning, with most stores shuttered down. Explosions and machine gun fire could still be heard by lunchtime and American helicopter gunships were flying low over the area.

Fighters from al-Sadr's al-Mahdi Army (search), some concealing their faces with Arab head gear, were crouching behind heavy machine-guns in some areas, firing toward American positions. Small bands of militiamen, mostly in their late teens or early 20s, took cover behind walls at street corners.

At least two columns of black smoke could be seen rising from the area of the clashes.

West of Baghdad, five unidentified bodies in Arab-style robes were found in a communal grave near insurgent-controlled Fallujah, residents said. The site was uncovered when dogs began to paw at the area, they said. Militants ordered people to leave.

A U.S. Black Hawk helicopter crashed shortly after takeoff Tuesday near the southern city of Nasiriyah, wounding three crew members, the military said. It was not immediately clear what caused the crash.

The Associated Press contributed to this report.