A suicide bomber in a lorry rammed his vehicle into the municipal headquarters near Kirkuk.
The attack on the northern Iraqi town of Sulaiman Bek came shortly after Baghdad's Green Zone came under mortar fire on Thursday morning.
Police said the dead in Sulaiman Bek included women and children and that at least 35 people had been hurt.
Many houses were brought down in the blast. Captain Farhad Shwani said police were pulling bodies from the rubble and that dozens had been killed or wounded.
The attack on Baghdad's Green Zone involved at least seven mortar bombs, causing smoke to rise from buildings near the Iraqi parliament and government offices.
It was unclear if there were any casualties.
On the other side of the Tigris river on Tuesday, 87 people were killed by a lorry bomb which also partly demolished a Shia mosque.
The Green Zone, on the west side of the Tigris, is Baghdad's most secure area but has been a frequent target for rockets and mortar bombs.
The strikes have become more common and more accurate recently.
A mortar attack last week killed one employee of a hotel in the zone. There were also a number of casualties in April and May.
On April 12, a suicide bomber killed one politician in the parliament building in the worst breach of security in the zone since the March 2003 invasion to topple Saddam Hussein.
In northern Baghdad, one soldier was killed and three wounded when their vehicle was attacked by a rocket-propelled grenade.
On Wednesday, four soldiers were killed when their convoy was struck by a roadside bomb in western Baghdad. Another soldier was wounded.
Two marines were also killed in the western Anbar province on Wednesday.
And two more US soldiers were killed in southwest Baghdad and four wounded when a bomb exploded near their vehicle.
The latest fatalities took the military's losses in Iraq since the March 2003 invasion to 3,536, according to the AFP news agency.