A double-bombing targeting traffic police in eastern Baghdad killed at least 18 people and wounded 52 others Wednesday.
An Iraqi police official said the first blast was from a car bomb. Moments later, a roadside bomb went off nearby as people rushed to the scene.
The official spoke on condition of anonymity because he was not authorized to speak to the news media.
The U.S. military said a roadside bomb exploded near an American patrol hours earlier in the same area but that there were no deaths or injuries.
Meanwhile, Prime Minister Gordon Brown said Wednesday that the British mission in Iraq will end no later than May 31, 2009.
Brown made the announcement during a news conference with Iraqi Prime Minister Nouri al-Maliki in Baghdad. He says he plans to provide details to the British parliament about troop withdrawal on Thursday.
Brown also called for the release without condition of five British hostages held since 2007.
Brown's announcement follows news that the Iraqi government issued a resolution calling for all non-U.S. troops to withdraw by the end of July.
Britain is the second-largest contributor to the international military coalition in Iraq after the United States. About 4,000 British troops are now in Iraq, mostly in the country's south.