The incident took place in Bannu area of the province targeting the vehicle of the former chief minister and Jamiat Ulema Islam Fazal candidate Akram Khan Durrani.
District Police Officer Bannu Khurram Rashid has said the incident took place as Durrani was returning from an election rally and explosives were detonated close to his vehicle with the help of remote control.
Another senior police official, Mohammad Tahir, said at least three policemen were among those wounded.
The officials have said the death toll has climbed at least four people while at least 32 others have sustained injuries and are undergoing treatment in the District Headquarter Hospital in Bannu.
No individual or group has so far claimed responsibility behind the incident.
This comes as a suicide bomber targeted the Awami National Party candidate Haroon Bilour on Monday.
According to reports, at least nineteen people including Mr. Bilour were killed in the attack.
The Tehrik-e-Taliban Pakistan had reportedly claimed responsibility behind the attack.