Benazir Bhutto killed in attack
Benazir Bhutto had been addressing rallies in many parts of Pakistan
News of her death was confirmed by a military spokesman and members of her Pakistan People's Party (PPP).
Ms Bhutto had just addressed an election rally in Rawalpindi when gunfire and an explosion occurred.
At least 15 other people are reported killed in the attack and several more were injured. Ms Bhutto had twice been the country's prime minister.
She had been campaigning ahead of elections due in January.
The BBC's Barbara Plett says the killing is likely to provoke an agonised response from her followers, especially from her loyal following in Sindh Province.
Ms Bhutto was key to her party, she was the focus of her party and she was a major political player amongst all those fighting for seats in the forthcoming elections, our correspondent adds.
The PPP has the largest support of any party in the country.
Analysts note that Rawalpindi, a garrison city, is seen as one of the country's most secure cities, making the attack even more embarrassing for the military authorities.
Scene of grief
The explosion occurred close to an entrance gate of the park in Rawalpindi where Ms Bhutto had been speaking.
Wasif Ali Khan, a member of the PPP who was at Rawalpindi General Hospital, said she died at 1816 (1316 GMT).
Supporters at the hospital began chanting "Dog, Musharraf, dog", referring to President Pervez Musharraf, the Associated Press (AP) reports.
Some broke the glass door at the main entrance to the emergency unit as others wept.
A man with a PPP flag tied around his head could be seen beating his chest, the agency adds.
An interior ministry spokesman, Javed Cheema, was quoted as saying by AFP that she may have been killed by pellets packed into the suicide bomber's vest.
However, AP quoted a PPP security adviser as saying she was shot in the neck and chest as she got into her vehicle, before the gunman blew himself up.