Almost eight kilogrammes worth of TNT explosives were used in the blast, Qazi Jamil, the capital city police officer (CCPO) for Peshawar, added.
Haroon Bilour's 16-year old son, Daniyal, who was accompanying his father in the gathering, was also among the injured.
The death toll is feared to go up as at least 20 of the injured have been stated to be in a critical condition.
His father, Bashir Bilour was also martyred in a suicide bombing targeting his rally in the fabled Qissa Khawani bazaar of Peshawar in December 2012.
Earlier this month, seven people including a candidate of the Muttahida Majlis-i-Amal were injured in an explosion during an election rally near Takhtikhel canal.
The ANP, which governed the Khyber Pakhtunkhwa province from 2008 to 2013, has been a continual target of militant groups operating in the northwest.
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"Six people include Pakistan Tehreek-i-Insaf chairman Imran Khan, Awami National Party leaders Asfandyar Wali and Ameer Haider Hoti, Qaumi Watan Party head Aftab Sherpao, Jamiat Ulema-i-Islam-Fazl leader Akram Khan Durrani and Hafiz Saeed's son Talha Saeed".
"This shows weakness of our security institutions and a conspiracy against transparent elections", he said in a statement.
Expressing grief over the incident, Imran Khan demanded from the authorities to bring the culprits to justice. "All political parties and their candidates must be provided proper security during their election campaigns by the State", Khan tweeted.
Meanwhile, Bilawal Bhutto Zardari said the attack was a threat to democracy and the democratic process.
Noting that he had remained with Haroon Bilour throughout the election campaign, Danial, nonetheless, urged party workers to not lose hope.