Pakistani officials say the senior officer heading the probe into last week's suicide attack on former Pakistani Prime Minister Benazir Bhutto has withdrawn from the case.

The home secretary of Sindh province, Ghulam Muhammad Mohtarem, says Manzur Mughal stepped down after Ms. Bhutto accused him of involvement in the alleged torture of her husband while in police custody in 1999.

Ms. Bhutto survived an assassination attempt last Thursday when suicide attackers struck near her convoy as it drove through the packed streets of Karachi, the capital of Sindh province, hours after she returned to Pakistan, ending years of political exile.

The twice-serving former prime minister has said extremist elements in Pakistan's political establishment were behind the attack, which killed 139 people.

Investigators have said they suspect two suicide bombers were responsible for the attack.

Some information for this report was provided by AFP and AP.