Lieutenant Colonel Talib of the Iraqi army said the attack occurred near the al-Kindi hospital.
"An improvised explosive device exploded inside a vehicle as it approached the hospital,” Talib said.
More than 10 other people were wounded in the attack, including five police officers.
Police say another five people, including three police officers, have lost their lives in other incidents in the Iraqi capital today.
The U.S. military say two U.S. soldiers have been killed in Iraq over the past 24 hours.
The attacks come as hospital patients, prison detainees, and security forces in Iraq began voting in parliamentary elections.
On 13 December, Iraqi voters living outside the country will begin casting their ballots at polling centers in 15 countries.
The main vote for the 275-member assembly will take place on 15 December.
RFE/RL's coverage, background, and analysis of Iraq's December 15, 2005, legislative elections.