At least 25 people were killed today when a suicide blast targeting a Shiite procession shook Pakistan's financial capital, Karachi. City police Chief Wasim Ahmed said 80 people were injured in the attack. The blast took place on M.A. Jinnah Road where thousands of Shiite devotees were commemorating Ashura, a major religious observance. Ashura marks the death anniversary of Imam Hussein, grandson of Prophet Mohammed. Hussein, who was killed in battle in Karbala in 680 A.D. Pakistan Interior Minister Rehman Malik said the suicide bomber had been walking with the procession, before detonating the explosives. Karachi police Chief Waseem Ahmed said the severed head of the bomber had been found. The bombing unleashed further pandemonium as angry Shia mourners fired shots in the air. Some marchers pelted the security forces that had been guarding the march with stones. Television footage showed smashed police vehicles and ambulances. Karachi Mayor Mustafa Kamal appealed for calm.