The death toll is the highest reported incident in Iraq for nearly one month.
Concrete blocks have been constructed and checkpoints have been set up nearby to prevent such an attack.
The bomb went off one hour after the demonstration had started and according to some sources the bomber had mingled with the crowd.
The police believe that the bomb was remotely detonated, despite speculation regarding a bomber committing suicide.
Some reports suggest a motorcycle crashed into the crowd and the rider detonated explosives in a worn belt.