A woman suicide bomber has killed six people at a bus station in Balad Ruz in Diyala province, Iraqi police say.
Dozens have died or been hurt in a string of attacks this week
A recent increase in attacks by female suicide bombers is partly due to the ease of concealing explosives under their clothing, correspondents say.
One of the dead was a policeman, a local officer said, and 12 more people were wounded including three policemen.
Elsewhere, US troops shot dead three Iraqi policemen by mistake near the northern city of Kirkuk.
If the attacker's identity is confirmed, it would be the eighth female perpetrator of a suicide bombing this year.
A US military statement described the incident in Kirkuk as a tragic accident, which was sincerely regretted.
The soldiers are thought to have opened fire after feeling threatened when the police drove at high speed into an area which had been cordoned off.
US and Iraqi forces launched major security operation in Kirkuk in November last year targeting alleged al-Qaeda in Iraq militants.
The latest deaths come a day before the fifth anniversary of the US-led invasion of Iraq, which has been battered by continuous violence since then.
President George W Bush is marking the date with a speech at the Pentagon in which he is expected to say he has no doubts about launching the war and toppling Saddam Hussein, despite the high cost in lives.
Nearly 4,000 US military personnel have died in Iraq as have more than 170 from Britain.
Tens of thousands of Iraqis have been killed, though there are no precise figures, and estimates vary widely.
Anti-war demonstrations are also expected in Washington.
Mr Bush is expected to warn against any retreat after recent improvements in security fuelled by the increase of 30,000 US troops in violence-hit areas.