The death toll in the suicide blast targeting the political rally in Mastung Friday jumped to 128, officials told AFP, in the deadliest attack in the country since 2014.
Bungalzai also confirmed the explosion killed Siraj Raisani, who was running for a provincial seat with Balochistan Awami Party (BAP).
A senior provincial government official also confirmed the figure, adding that 150 others were injured in the attack.
The Islamic State group claimed responsibility for the attack.
Durrani, who was heading back from an election rally near North Waziristan, remained safe in the remote control blast, District Police Officer (DPO) Bannu Khurram Rasheed said.
Siraj, the younger brother of former Balochistan chief minister Aslam Raisani, was attacked during a corner meeting organised for the promotion of his candidature.
Mr Raisani was the brother of the former Baluchistan chief minister, Aslam Raisani.
"There seems to be a conspiracy to sabotage the 25 July elections but the people of Pakistan will not allow any design meant to target these historic elections to succeed", he continued.
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On Tuesday, a bomb claimed by the Tehreek-i-Taliban Pakistan (TTP) militant group targeted a rally by the Awami National Party (ANP) in the city of Peshawar.
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.
The Islamic State group has a muted presence in Pakistan but has carried out brutal attacks there in the past, including the blast at a Sufi shrine in February a year ago which killed almost 90 people.
Before that, on 7 July, seven people, including a candidate of Muttahida Majlis-e-Amal, were injured when a convoy came under a bomb attack in Bannu.
Expressing concerns over such attacks during election campaigns, he called for serious investigations in these attacks.
Pakistan's third major political movement, the Pakistan Peoples Party, joined the criticism of the crackdown, with its prime ministerial candidate Bilawal Bhutto Zardari questioning why Sharif's supporters would be prevented from gathering.
Analysts warn however that Pakistan has yet to tackle the root causes of militancy.