Iraqi officials say a roadside bomb blast has killed six people and wounded 12 others in the southern city of Basra.
Provincial officials say Sunday's attack seemed to target a U.S. military convoy, but hit a civilian bus instead. Authorities say women and children are among the victims, but the number is unclear.
Under the 2008 security agreement between the United States and Iraq, all American troops must leave the country by the end of the year. There currently are about 50,000 U.S. troops stationed in Iraq, mainly in a non-combat role.
Overall, violence has declined in Iraq from the height of sectarian conflict several years ago. But militants still carry out bombings and shootings almost daily.
Meanwhile, unknown gunmen raided a local radio station in the Kurdish region of northern Iraq and broke some equipment. No one was injured.
The Voice radio station in the town of Kalar is the second media outlet to be attacked in the north since protests erupted last month in the main city of Sulaimaniyah against the region's two major Kurdish political parties.
Both media outlets had been covering the demonstrations, in which protesters have been demanding political reform from the dominant parties in the Kurdish autonomous region.
On February 20, masked men wearing military-style clothes attacked a local television station that had aired footage of a deadly protest against the dominant political bloc. Station officials said the attackers shot and wounded a guard before firing at equipment and fleeing the scene.
Some information for this report was provided by AP, AFP and Reuters.