Military officials have reported the possibility of attacks by insurgents over the holiday period, similar to attacks in the capital on Christmas Day.
A car bomb exploded as a U.S. convoy passed on a street in the Iraqi capital full of shops, destroying one Humvee, Iraqi police Sgt. Thabet Talib said. An 8-year-old Iraqi boy was killed and 11 other Iraqi bystanders were being treated for injuries, hospital doctors said.
A spokesman for the U.S.-led coalition said he could confirm only that there was an explosion.
Elsewhere, gunfire erupted as hundreds of Arab and Turkmens marched in protest over fears of Kurdish domination in the oil-rich northern city of Kirkuk, and police said two people were killed.
Also Wednesday, U.S. military officials reported a U.S. soldier was killed and a second wounded in the accidental discharge of a weapon. A statement said the accident, in the 82nd Airborne Division, occurred Tuesday evening at Tanf, on Iraq's western border with Syria.
It was the 478th U.S. death in Iraq.
In other developments:
In Kirkuk, it was not immediately clear who fired the shots into hundreds of Arabs and Turkmen demanding that the city remain under a central Iraqi government and not be incorporated into any proposed Kurdish area.
"Kirkuk is an Iraqi city!" protesters shouted.
Police Col. Salem Taha said Kurdish gunmen opened fire as demonstrators opposed to Kirkuk joining a Kurdish federation tried to converge on the office of the Patriotic Union of Kurdistan party.
But a party official, Jalal Jawher, said armed men who had infiltrated the protest fired at his party office and police guarding the building returned fire.
"We did not open fire on the protesters. Not a single shot was fired from our building," Jawher said. The official said his party was not opposed to the demonstration.
Two protesters were killed and 16 were wounded in the shooting, said Taha, the police colonel. Records at Jumhouri Hospital showed 26 wounded people were admitted Wednesday.
U.S. soldiers moved in with tanks to barricade the area and set up checkpoints at major intersections.
Residents of Kirkuk are divided in roughly equal parts among three ethnic groups — Arabs, Turkmen and Kurds.
Some Kurds in Kirkuk have been calling for the city to become part of an autonomous Kurdistan, joining a Switzerland-sized area of northern Iraq where Kurds have ruled themselves since the end of the 1991 Gulf War under U.S.-led aerial protection.
Under the regime of Saddam Hussein, Iraq's Sunni Arab minority dominated the country. The Shiite majority is largely centered in the south, while Kurds dominate the north.
The Governing Council, selected by U.S. administrator L. Paul Bremer to reflect the size of the country's diverse groups, has 13 Shiites, five Arab Sunnis, five Kurdish Sunnis, one Turkman and one Christian.
The U.S.-led coalition plans to transfer authority to a transitional Iraqi government by July 1.
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