The attack occurred at 9.30am (6.30 GMT) in the busy central Baghdad neighbourhood, which includes a medical complex, the health ministry and the central morgue.
The bomb detonated near street vendors close to the ministry building, security officials said.
In southeast Baghdad, at least one civilian was killed and eight people were injured by another roadside bomb.
A truck was struck by the bomb in the early morning attack.
A third attack consisted of two co-ordinated explosions in the al Waziriyah district of northern Baghdad, police said.
The first explosion injured two civilians and a second killed one soldier and wounded six others, as they arrived at the scene.
The bombings follow a relative lull in attacks in the Irali capital in recent months, after a US troop "surge".
All types of attacks in Iraq have dropped by 55 per cent since the "surge" became fully operational in June, Gregory Smith, the US military spokesman, said.