A car bomb targeting an Iraqi police station in the northern city of Mosul has killed at least five people and wounded about 50 others.
Fighting in Falluja has been fierce in recent days
Many of the casualties were police, hospital sources say.
Over the past year Iraqi insurgents have repeatedly attacked security forces, whom they view as collaborators supporting US forces.
The attack came as more clashes between US forces and insurgents were reported in the flashpoint city of Falluja.
The Mosul blast occurred when a 4X4 vehicle drove at speed into a restricted entrance outside the police station early on Sunday, a policeman at the scene told AP news agency.
The vehicle was fired upon by police, came to halt and exploded, he said.
Those killed are reported to include two Iraqi civilians and two Iraqi policemen.
Doctors said they expected the death toll to rise.
Last month Mosul's governor was killed in a grenade attack.
The latest blast comes four days after 70 people were killed in a suicide bombing outside a police base in Baquba, north-east of Baghdad.
In a separate incident, at least 10 Iraqis were killed and 36 wounded in overnight fighting in Falluja, west of Baghdad.
Residents described explosions and heavy clashes in eastern parts of the city, as US marines used tanks and aircraft against militants.
The US military has conducted a number of air strikes on Falluja in recent weeks, in which it said dozens of suspected
militants had died.
The Americans say the city is being used by fighters loyal to Abu Mussab al-Zarqawi, a Jordanian-born militant linked to al-Qaeda.
He is accused of masterminding a large part of the violence around Iraq.
A US soldier died on Sunday in Samarra, some 60 miles (100km) north of Baghdad, when a roadside bomb exploded as a patrol drove past, the military said.
In Baghdad, another roadside bomb killed two civilians and wounded two others late on Saturday.
The bomb is said to have gone off shortly after an American convoy went past.