The car exploded outside of the police compound in Baquba, 40 miles north of Baghdad, according to witnesses. The U.S. military reported five deaths and 29 wounded, but doctors in Baquba said only two were killed. It was also unclear whether the bomb was a suicide attack.
Police at the scene said they saw the bomber coming toward the compound, his foot strapped to the accelerator, ensuring the car would speed ahead and detonated even if he were shot and killed before the explosion.
A U.S. military spokeswoman said later, however, that the car was packed with grenades and mortar bombs and detonated remotely.
The attack came after a raid by U.S. troops in Samarra, 60 miles north of Baghdad, which resulted in the capture of four nephews of Izzat Ibrahim al-Douri, number six on the most-wanted list -- the first five on the most-wanted list have either been killed or captured.
Soldiers from the 720th Military Police Battalion based in Fort Hood, Texas, seized the nephews in two houses. One of the targeted nephews and his two brothers were captured in one house, and the other targeted nephew was in a home nearby.
It is believed that the two targeted nephews have helped al-Douri hide by finding him safehouses, Col. David Poirier of Chicago told an Associated Press reporter.
"They have information they can provide to us ... that would be extremely important," Poirier said. "One of these days his (al-Douri's) head will rise up above the water, and we will be able to capture him as well."
With a $10 million bounty on him, al-Douri is said to have been behind some of the attacks on U.S. troops in the last eight months.
U.S. authorities also announced Wednesday that they had captured number 54 on the most-wanted list.
"As a result of aggressive operations this week, the coalition announces the capture of Khamis Sirhan al-Muhammad, number 54 on the most wanted list." Brig. Gen. Mark Kimmitt told a news conference in Baghdad.
U.S. officials have described al-Muhammad, a former regional party leader in Karbala, as the paymaster for insurgent forces in Anbar, Iraq's largest province containing such hotspots as Fallujah and Ramadi.
In a non-hostile incident in northern Iraq, an American soldier from the 101st Airborne Division died Tuesday, according to the U.S. military, raising the U.S. death toll from the start of the war in March to 496.
Also on Tuesday, a U.S. helicopter was reportedly shot down in the Sunni Triangle, the heart of the guerilla war, but both crew members on the helicopter survived. U.S. officials said it could have been shot down by enemy fire. It was the third helicopter in that area to come down in less than two weeks.