At least three people were killed and 30 injured on Tuesday night in Pakistan's commercial capital Karachi in a bomb blast targeting a roadside camp office of the Muttahida Qaumi Movement (MQM).br br The political party temporarily closed down all its Karachi offices and called for a day of mourning in response to the attack.br Karachi police believe that the perpetrators waited for a crowd to gather near a party banner, torn by unidentified men, before setting off the bomb.br br An explosive device containing ball bearings and nuts and bolts was placed in a flower pot underneath the torn party banner and detonated remotely. br br The blast left a crater measuring a third of a meter deep and a meter wide.