At least seven people have been killed by a suicide bomber in Miqdadiya, north of Baghdad, Iraqi officials say.
It is a year since US troop numbers were increased to boost security
In other attacks, four policemen died in the northern Iraqi city of Mosul and a suicide car bomber killed a woman in Talafar near the border with Syria.
A roadside bomb killed three US soldiers in Baghdad, the US military said in a statement on Wednesday.
US and Iraqi forces have been cracking down on militant groups and anti-US insurgents in the past 12 months.
US commanders say the overall level of attacks on their troops has fallen, although 22 American soldiers have been killed in February according to media reports.
Details are still coming in about the Miqdadiya bombing, which occurred in a market in the town in Diyala province.
Both Diyala and Mosul are the focus of military operations to curb the activities of Sunni Muslim militants.
Earlier, Iraqi officials said 15 policemen were killed late on Tuesday and more than 45 were wounded in eastern Baghdad when an insurgents' truck with a multiple rocket launcher on board exploded.
Iraqi police officials initially said a bomb disposal team had been trying to defuse unfired rockets on the launcher in the Obeidi area when "a mishandling" caused a powerful explosion.
However, this was later contradicted by interior and defence ministry officials, who said explosives placed in the vehicle had been detonated by remote control.
"This was a well-planned ambush," said an interior ministry official quoted anonymously by AFP.
Some rockets had already been fired at a nearby US military base, where four soldiers were wounded, a US military statement said.
The rocketing was the second such attack in two days in Baghdad. Five Iraqis were killed on Monday.
US military official have said rogue Shia groups backed by Iranian Revolutionary Guards were behind the recent spate of attacks, using stocks from hidden arms stockpiles.