Saturday's protests were sparked by last week's bombing of Bhutto's homecoming motorcade that killed more than 139 people celebrating her return from eight years of exile, CNN-IBC reported Sunday.

Police say as many as five people may have been responsible for the bombing, Dawn reported Saturday. The suicide bomber may have been part of a suspicious-looking group of men seen holding sticks, a senior police official told Dawn.

Bhutto blamed the bombing on supporters of Pakistan's late military ruler Mohammed Zia ul-Haq. Zia overthrew Bhutto's father, Prime Minister Zulfikar Ali Bhutto, in 1977 and had him hanged two years later. Zia died in a plane crash in 1988.