A series of suicide bombings shook the northern Iraqi city of Baquba Wednesday, killing at least 31 people and injuring 48.
The three-stage attack is the deadliest in recent weeks and comes just days before Iraqis vote in parliamentary elections.
Police say the first two bombers drove explosive-packed cars and struck near government buildings and police stations. A third assailant rode in an ambulance with victims of the first two bombings and blew himself up at the city's emergency hospital.
So far, no group has claimed responsibility. Iraqi police imposed a curfew immediately following the attacks and say they have four suspects in custody.
Both U.S. and Iraqi officials have warned insurgents would increase attacks in an attempt to disrupt the vote.
Iraqi officials said many of those killed in Wednesday's attack were policemen sent to help secure the area for the elections.
The March 7 vote is just the second parliamentary ballot since the overthrow of former dictator Saddam Hussein in 2003.
It is considered a test of Iraq's ability to maintain its own security and conduct a smooth transition of power after years of war and sectarian fighting.
Pentagon spokesman Geoff Morrell said Wednesday that despite the recent violence it would, in his words, "take an extraordinarily dire turn of events" for the U.S. to slow down its planned withdrawal of troops from Iraq.
Baquba is about 60 kilometers northeast of Baghdad and is the capital of Diyala province.