In Kirkuk, a huge suicide truck bomb in coordination with four other vehicle bombs killed 23 people and wounded 77 others.
Mortars and car bombs killed five in the city of Fallujah, in Iraq's biggest and most volatile province of Anbar, where US forces are being reduced to reinforce Baghdad.
In the deadliest blast on Sunday, a suicide attacker driving a truck rigged with explosives blew himself up outside a police centre killing 17 people, mostly civilians, police said. The toll included 10 women and two children who were visiting relatives.
Within an hour, a car bomb targeting a US military patrol killed three civilians and wounded six in the city. Minutes later, another suicide car bomber rammed into an Iraqi army checkpoint, wounding two soldiers. Two other car bombs followed.
Sherko Shakir, Kirkuk's police chief, said the near simultaneous explosions, among the worst violence in the city in months, were intended to "destabilise the city".
The US military called the mortar and car bomb attacks directed at a US military centre in charge of reconstruction in Fallujah "complex and coordinated". The five killed there included two Iraqi police and one Iraqi soldier. No US casualties were reported in the attack, which wounded 23.
US commanders are diverting troops to Baghdad from Anbar province for a month-old crackdown in the capital, which they see as the key to securing the country.
That tactic has been questioned after a leaked US Marine intelligence report said Washington would need another division to defeat insurgents in Anbar, heartland of the Sunni Arab insurgency and the deadliest province for US troops.
A roadside bomb in a popular bird and animal market in Baghdad killed two people and wounded eight, police said.
US and Iraqi officials say sectarian violence between the majority Shia and Sunnis is a greater threat to Iraq's survival than the three-year-old Sunni insurgency US-led forces have been fighting mainly west and north of Baghdad.