A suicide bombing in central Baghdad has killed at least three Iraqis and a US soldier.
The police are frequent targets of insurgent violence
Police say the bomber appeared to be targeting an American military patrol in Tayaran Square.
Before the area was sealed off by troops, eyewitness reports said US soldiers might be among the wounded.
Earlier, 10 Iraqi policemen and a number of civilians were killed in a spate of drive-by shootings, most of them in the capital.
Tayaran Square, which was hit at about lunchtime, lies in a busy part of Baghdad and is usually full of people waiting for buses.
Five civilian cars, a US Army vehicle and a four-wheel drive were reported damaged in the blast. At least 91 Iraqis were injured, medical sources said.
Earlier, five officers died in a drive-by shooting in east Baghdad as they slept in their car after a night shift.
Police officers and recruits are a common target of insurgent attacks, but correspondents say this attack marks a change of tactics from the insurgents.
Two carloads of gunmen opened fire as they sped past a police four-wheel drive.
The five officers inside were asleep as they awaited replacement after a nightshift at around 0800 local time (0400 GMT).
Their weapons were all in the backseat, a report from the scene said.
About 15 minutes later, two officers were killed and their driver was wounded in the nearby Zaytouna district.
An attack in the Dura neighbourhood, in south Baghdad, killed police captain Haidar Mizhir Salih and another policeman, a local officer said.
In Baquba, a police lieutenant said one officer was shot dead and another was wounded in a nearly simultaneous attack.
Three Shia pilgrims heading to Iran were also killed and eight injured when attackers sprayed their vehicle with gunfire near the town, medical sources said.