Forensics lab hit
The attacker managed to evade tight security in the central neighbourhood of Karrada, where checkpoints are located at all the entrances and police conduct regular security searches.
Major General Qassim Atta, an Iraqi military spokesman in Baghdad, said the attack targeted the forensics institute, which has been bombed twice before.
"At 10.45am (0745 GMT) a suicide bomber raced his vehicle towards the institute", Atta said.
"The building collapsed soon after the explosion. Dozens of people usually work in the institute," he said.
The interior ministry official said the blast wrecked the laboratory.
The blast comes a day after three huge minibus bombs exploded across the capital killing dozens of people.
Those blasts targeted well-known hotels and came on the same day that the government announced the execution of "Chemical" Ali Hassan al-Majid, a cousin of Saddam Hussein, the ousted former president.
Iraqi politicians and US forces have warned of rising violence ahead of the March 7 elections, the second parliamentary ballot since the 2003 US-led invasion that ousted Saddam.