al-Qaeda has taken responcibilty for the assassination of pakistani politician Benazir Bhutto at an election rally on Thursday.
Citing what it said was an intercepted phone call, the interior ministry said the killing had been ordered by "al-Qaeda leader" Baitullah Mehsud.
The BBC's security correspondent, Frank Gardner, says it is too early to establish the truth of what happened.
Ms Bhutto has been buried in her family tomb amid scenes of mass grieving.
Video of her last moments before the attack in Rawalpindi was shown at the news conference given in Islamabad by the interior ministry.
Pakistani security forces are on high alert, with at least 19 people killed in protests by Bhutto supporters across the country since the assassination