A suspected suicide attack at a rally of Benazir Bhutto's Pakistan People's Party (PPP) has left at least 15 people dead, police say.
The blast happened by an entrance to a park
A PPP spokesman has told the BBC that Ms Bhutto was injured. It is not clear how badly. She had just addressed the rally in the town of Rawalpindi.
National and provincial assembly elections are due on 8 January.
In October some 130 people were killed in an attack on Ms Bhutto's cavalcade when she returned to the country.
It was one of the worst incidents of violence in a year of deteriorating security in Pakistan.
Thursday's blast happened at one of the entrance gates to the Liaquat Bagh park in Rawalpindi.
Benazir Bhutto on the campaign trail
PPP spokesman Farahtullah Babar said Ms Bhutto was only some 50 metres away when the bomb exploded, the Associated Press news agency reports. "She had just crossed the gate when we heard a deafening sound."
Mr Babar said that Ms Bhutto was safe, but subsequently PPP party members have said that Ms Bhutto was injured in the blast and taken to hospital.
Ms Bhutto returned from self-imposed exile in October after years out of Pakistan where she had faced corruption charges.
Her return was the result of a power-sharing agreement with President Musharraf in which he granted an amnesty that covered the court cases she was facing.
Since her return relations with Mr Musharraf have broken down.
On the day of her return she led a motor cavalcade through the city of Karachi. It was hit by a double suicide attack that left some 130 dead.
The PPP has the largest support in the country.
Earlier on Thursday at least four people were killed ahead of an election rally that Pakistan's former Prime Minister Nawaz Sharif was preparing to attend close to Rawalpindi.