Other violence in and around Baghdad on Monday killed another six people, bring the total to nine. A total of 21 people were injured.
The minibus attack, Lieutenant Mohammed Khayoun of the Baghdad emergency police said, exploded near the al-Kindi hospital and east Baghdad's Nadhaa bus station. The driver of the van abandoned it on the street and ran, he added.
All three killed were Iraqi civilians, and the wounded included five police officers, he said.
In Baghdad, police said that a number of clashes between unidentified armed men, police and the Iraqi army resulted in the death of two police officers and injuries to another nine.
Separately, a police sergeant was reportedly killed by an American patrol, police Captain Taleb Thamer said.
In Muqdadiya, about 90km north of Baghdad, a roadside bomb killed an Iraqi woman and injured five other people.
Police said a businessman, identified as Mohammed Yousif, 43, was kidnapped along with his 23-year-old son in Baghdad's al-Mansur district. No other details were available.
Defaced election posters point to
the threat faced by Iraqi voters
Another two people were killed in an early morning drive-by shooting in Baghdad's southern al-Dura district.
Thirteen prisoners suffered abuse serious enough to require medical treatment while at a detention centre operated by the Iraqi Interior Ministry special commandos in Baghdad, The Washington Post reported on Monday.
In a dispatch from Baghdad, the report cited US and Iraqi officials as saying "an Iraqi official with firsthand knowledge of the search said that at least 12 of the 13 prisoners had been subjected to severe torture, including sessions of electric shock and episodes that left them with broken bones".
"Two of them showed me their nails, and they were gone," the report said, quoting the official, who it said was not named because of security concerns.
US officials warn of an upsurge in
violence in advance of the vote
Iraqi government spokesman Laith Kubba said late on Sunday that any findings at the prison would be "subject to an investigation".
However, Kubba declined to comment on the allegations, the newspaper reported.
The site, which was searched on Thursday, is the second Interior Ministry detention centre where cases of prisoner abuse have been confirmed by US and Iraqi officials, the report added.
International law, including the UN Convention Against Torture, bans torture in all cases.