The Pakistani government has said it has evidence al-Qaeda was responsible was for the assassination of Benazir Bhutto, the former prime minister who was buried earlier on Friday.

Javed Cheema, an interior ministry spokesman, said security forces had intercepted a phone call from an al-Qaeda leader in Pakistan after Bhutto's death on Thursday.

"We have intelligence intercepts indicating that al Qaeda leader Baitullah Mehsud is behind her assassination," Cheema said.

Violence continued to grip Pakistan following Bhutto's funeral in the southern province of Sindh, with the death toll from disturbances across the country rising to 31.

Cheema also said Bhutto had died from injuries caused by hitting her head on her car's sunroof as she came under fire, rather than from gunshot wounds or shrapnel.

Bhutto was reported to have been gunned down by an assassin who then blew himself up in an attack that killed a total of 16 people at the end of an election campaign rally in Rawalpindi on Thursday.

An aide to Benazir Bhutto also described the governments explanation as "a pack of lies."

"Two bullets hit her, one in the abdomen and one in the head,"  said Farooq Naik said, a senior official in her Pakistan People's Party. 

"It is an irreparable loss and they are turning it into a joke with such claims. The country is heading towards civil war."

And Kamal Hyder, Al Jazeera's Pakistan correspondent, said people were asking why the car Bhutto was travelling in was not damaged by Thursday's attack.

"A lot of people in Pakistan believe there may be some kind of conspiracy behind the assassination."

Questions have also been raised about why the scene of the attack that killed Bhutto was hosed down by the authorities soon after the blast, a move that may have destroyed valuable evidence.

Cheema also said was also behind a suicide attack on a Bhutto rally in October that left 140 dead.

Pakistani authorities say Mehsud is based in the tribal region of South Waziristan.

Grieving supporters

Hundreds of thousands of mourners gathered on Friday for the funeral in front of the mausoleum in Garhi Khuda Bakhsh, a village 5km from the Bhutto home in the small town of Naudero in Larkana district.

Bhutto, 54, had been hoping to lead the PPP to victory in the January 8 parliamentary election, having been prime minister twice before.

Supporters arrived by tractors, buses, cars and jeeps that were parked in dusty fields surrounding the mausoleum - a vast, marble structure.

Weeping in grief and chanting slogans against figures in the pro-government political party, they formed into hundreds of rows for the funeral prayers.

Asif Ali Zardari, Bhutto's husband, accompanied the closed coffin draped with the PPP's green, red and black tricolor as it began the 7km journey by ambulance.

Some protesters chanted defiance: "No matter how many Bhuttos you will kill, a Bhutto will emerge from each house."

Bhutto had returned to Pakistan from Dubai in October, ending more than eight years of self-imposed exile after reaching an understanding with Pervez Musharraf, the Pakistan president.

She survived a suicide-bomb attack during her homecoming procession in Karachi that left about 140 supporters dead.

Election fears

There are fears that the January 8 polls will not now go ahead after Nawaz Sharif, another opposition leader and former prime minister, said he would boycott the poll.

The PPP also said it would observe a 40-day period of mourning.

Ameen Jan, a Pakistani political analyst, told Al Jazeera that the PPP also needed to find a new leader to achieve its political goals.

"In terms of leadership contenders, there are several, including Makhdoom Amin Fahim, the vice-chairman, who, since yesterday,  became the person holding the reigns."

 PHOTO CAPTION

Rioters in Peshawar on 28 December