Updated at 12:07 p.m. Eastern.
Three suicide bombers including one who sneaked his explosives into a hospital killed at least 32 people Wednesday in a former insurgent stronghold northeast of Baghdad, sending a deadly signal ahead of Iraq's weekend elections.
Deputy Interior Minister Iden Khalid said at a news conference afterward in Baghdad that security forces expect further attacks, but they will not interfere with Sunday's vote.
The blasts struck Baqouba in quick succession, starting with a suicide car bomb that targeted a local government housing office near an Iraqi army facility, police spokesman Capt. Ghalib al-Karkhi said.
Within minutes, a second suicide car bomb exploded 200 yards (meters) down the street near the provincial government headquarters near many police and army personnel.
It was the final bomber, however, who caused the most casualties, by donning a military uniform, pretending to be wounded and riding an ambulance back to the hospital where he blew himself up, said al-Karkhi, killing many of the wounded from the first two bombs.
Police later safely detonated a fourth car bomb about 220 yards (200 meters) from the hospital.
Insurgents often carry out multiple bomb attacks to maximize damage as rescuers and others rush to the scene to help those affected.
The blasts come just ahead of Sunday's crucial ballot to decide who will oversee the country as U.S. forces go home. At stake is whether Iraq can overcome the deep sectarian tensions that have divided the nation since the 2003 U.S.-led invasion.
U.S. and Iraqi officials have warned of a possible uptick in violence ahead of the weekend as insurgents seek to disrupt elections. A message last month purported to be from the leader of the al Qaeda front in Iraq promised just that.
No group immediately claimed responsibility for the bombings, but such attacks have been the hallmark of al Qaeda in Iraq. Police said they arrested four suspects and imposed an open-ended curfew on the city as they search for more suspects.
Mahmoud Fadil, 50, said he was heading to the electric company office when he heard an explosion and was thrown through the air.
"I saw others covered with blood lying on the ground and some crying because of wounds caused by shrapnel and the huge blast," he said.
Spokesman Fakhri al-Obaidi of the Diyala provincial council said the bombings reflected a "major security failure," shattering a period of relative calm in the province that was once a byword for savage sectarian fighting.
"These attacks aim to terrify people from going to polling stations, but I am sure that people will insist on voting," he said.
Wednesday's bombings were the deadliest since the start of February, when a female suicide bomber blew herself up at a way station for Shiite pilgrims also in Diyala, 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.
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 and hundreds of thousands of police and army troops deployed across the country.
Baqouba, 35 miles (60 kilometers) northeast of Baghdad, is the mixed Shiite-Sunni provincial capital of Diyala. The whole area was a flashpoint in the insurgency, although it has quieted since 2007.
Also on Wednesday, a senior official in Iraq's Independent High Electoral Commission said the results of Sunday's vote would not be announced quickly because of the time required to collect votes from abroad and investigate any complaints. He did not estimate when results would be released.
In Babil province south of Baghdad, police arrested 33 people for distributing leaflets calling for a boycott of the election because it is "supervised by the Americans," a police official said. He spoke on condition of anonymity because he was not authorized to speak to the media.
While Sunni leaders did talk of a boycott, they appear to have discarded the idea, despite the ban of hundreds of candidates for alleged ties to Saddam Hussein's former ruling Baath Party. The ban is supervised by a Shiite-led committee, widely believed to be biased against Sunnis.