At least 18 people have been killed in a series of bomb blasts around a town in northern Iraq, police say.
The attacks seemed to be aimed at checkpoints
Four devices exploded within minutes of each other, three of them suicide bombs near army checkpoints in and around the troubled town of Hawija, near Tikrit.
Some victims were Iraqi soldiers. Insurgents often target local and foreign security forces.
A suicide bomb attack was also reported near a police patrol in the Shula district of northern Baghdad.
At least 27 people were injured in the blast, many of them passers-by, although it is not thought anyone apart from the bomber was killed.
The US military reported on Tuesday that two marines had been killed since Sunday in roadside bombs near the western city of Falluja.
Meanwhile, officials said almost 900 suspected militants had been arrested in the past two weeks as part of a drive to reduce attacks in Baghdad.
They said they had succeeded in setting up more checkpoints to control the roads leading into Baghdad, and begun to push militants out of the capital.
The attacks in Hawija began with a roadside blast in the town.
Within seven minutes that was followed by suicide car bombings at checkpoints in Bagara and Dibis - towns close to Hawija - and at a checkpoint in Hawija itself.
At least 19 people were reported wounded in the blasts.
"I was standing some distance from the checkpoint when I heard a big explosion and I was thrown onto the ground," Lt Sadiq Mohammed, 26, who was injured in the Dibis attack, told AP.
"This is a terrorist act because real resistance should only target American troops, not Iraqis trying to protect their country."
The car bombings appeared to be co-ordinated, police Col Ahmed Hammoud told the Associated Press news agency.
He said that they were all carried out in a similar way, with the drivers waiting in queues of traffic before blowing themselves up at the checkpoints.
A fourth car, which had been packed with explosives and left in a nearby village, was being dealt with by Iraqi troops and US soldiers.
Casualties from the attacks were transported to the main hospitals in Hawija and Kirkuk, Yarub al-Sumaidi, a medic in Hawija's general hospital, told AFP news agency.
US forces have now sealed the town and Apache helicopters are flying overhead, the agency reported.
On 11 May, a suicide bomber struck outside an army recruitment centre in the town killing 32 and wounding 28.