City police chief Azhar Farooqi said a grenade was thrown in the crowd to create panic just before the suicide bomber blew himself.

Bhutto had been waving to the crowds for hours while standing on the truck and the explosion occurred destroying at least two police vans just as she had just climbed down, a Karachi policeman man.

Witnesses said they heard an explosion, which was followed within a minute by a bigger one that tore through a police van that was ahead of the armoured truck in which Bhutto was travelling with her close aides.

At the blast site, bodies of men in traditional white dress lay surrounded by burnt metal and other debris.

The Pakistan government had earlier warned Bhutto that she faced a threat from pro-Taliban militants, especially rebel leader Baitullah Mehsud who had warned that his suicide bombers will be waiting to 'receive' the former premier.

Bhutto had, however, said no true Muslim would dare attack a woman.

Image: The blasts left behind a trail of destruction. Image: Sonny Tumbelaka/AFP/Getty Images