U.S. and Iraqi officials have warned repeatedly that insurgents were expected to launch such attacks in an attempt to disrupt the crucial vote. A man purporting to be Abu Omar al-Baghdadi -- the leader of an al-Qaida front group in Iraq -- has vowed to violently disrupt the vote.
The bombings could also affect the candidacy of Prime Minister Nouri al-Maliki, who came to power in 2006 and oversaw a return to relative stability in 2008 and 2009. Al-Maliki has continued to bill himself as the best candidate to assure security in Iraq.
A police spokesman in the volatile Diyala province, Capt. Ghalib al-Karkhi, said the blasts struck in quick succession in Baqouba, 35 miles (60 kilometers) northeast of Baghdad, and also wounded 48 people.
First, a suicide car bomb targeted a local government housing office next to an Iraqi Army facility. Within minutes, another suicide bomber blew up a vehicle about 200 yards (meters) down the street from the first blast at an intersection near the provincial government headquarters where many police and army personnel were located, al-Karkhi said.
A third suicide bomber, wearing an explosives vest, rode in an ambulance with the wounded to the city's emergency hospital and blew himself up as rescuers and victims from the first two blasts were being rushed in for treatment, he added.
Most of the victims came from the blast at the hospital, al-Karkhi said. Police later safely detonated a fourth car bomb about 220 yards (200 meters) from the hospital.
An official in the Diyala police department who did not want to be identified because he was not authorized to speak to the media confirmed the death toll.
Insurgents often spread out bomb attacks as a way to maximize damage as rescuers and others rush to the scene to help or ferry the victims to hospital for treatment.
No group immediately claimed responsibility, but such attacks have been the hallmark of al-Qaida in Iraq. Police said they arrested four suspects and imposed an open-ended curfew on the city as they search for more suspects.
One witness in Baqouba described being thrown against a nearby wall by the first blast and said that immediately after the explosion, Iraqi security forces began firing their weapons. The witness said she hid in a nearby building, then when the situation appeared to have calmed down, went outside only to hear another blast go off seconds later.
"The place was covered with dust and the smell of TNT powder was all over the area, where panicked people were running and cars were colliding with one another," said the witness. She spoke on condition of anonymity out of security concerns.
The provincial police chief, Maj. Gen. Abdul-Hussein al-Shimari, was in the hospital at the time of the blast, but was unharmed, al-Karkhi said.
Deputy Interior Minister Iden Khalid said at a press conference later Wednesday in Baghdad that security forces expect further attempts to carry out attacks, but that the security situation will not interfere with Sunday's vote.
Wednesday's bombings were the deadliest since the start of February, when a female suicide bomber detonated her explosives inside a way station for Shiite pilgrims marking an important Shiite religious occasion, killing 54 people. At the time, Baghdad's top security official said extremists were adopting new methods to outwit bomb-detection squads such as stashing explosives deep inside the engines and frames of vehicles.
In January, a two-day wave of suicide car bombers struck three hotels in Baghdad and the city's main crime lab, killing at least 63 people.
Iraqi authorities have vowed tight security in the capital and the rest of the country in the run-up to the election and on voting day. Generally a vehicle ban is imposed across Iraq, the airport will be shut down on Sunday and hundreds of thousands of police and army troops dispersed across the country.
Baqouba is a mixed Shiite-Sunni city and Diyala's provincial capital. Both the city and the province were flashpoints of the insurgency, although they have quieted since the height of attacks in 2006 and 2007.