A suicide car bomber exploded his vehicle in central Baghdad, killing at least five people and destroying the government's forensics headquarters, an interior ministry official said.
The explosion also injured at least 20 people, with the toll expected to rise as many people were believed to be in the building at the time, the official said.
"The building collapsed soon after the explosion. Dozens of people usually work in the (forensics) institute," he added, speaking on condition of anonymity.
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The blast, in Karrada neighbourhood, came a day after three huge and apparently co-ordinated minibus bombs targeted hotels in Baghdad, killing at least 36 people and wounding 71.
Iraqi politicians and US forces have warned of rising violence ahead of the March 7 vote, the second parliamentary ballot since the 2003 US-led invasion ousted Saddam Hussein but ushered in a deadly and long-lasting insurgency.
The hotel bombings came on the same day the government announced that Saddam's notorious cousin and henchman "Chemical" Ali Hassan al-Majid, a symbol of the fallen regime, had been executed.
