A local candidate was among the dead in the Mastung town, police say. So-called Islamic State (IS) claimed the attack.
Earlier, a bomb attack on a similar rally in the northern town of Bannu killed four people. The attacks come ahead of general elections on 25 July.
Meanwhile, former PM Nawaz Sharif was arrested after flying home from the UK.
Sharif and his daughter Maryam were taken into custody by officials from the National Accountability Bureau (NAB) after landing in the northern city of Lahore. They were then put on a chartered plane bound for Pakistan’s capital Islamabad.
They were later transferred to a local prison.
The three-term PM was ousted last year after a corruption investigation. Last week he was sentenced in absentia to 10 years in prison.
He has accused Pakistan’s powerful security establishment of conspiring against him ahead of the elections.
“Mir Siraj Raisani succumbed to his wounds while he was being shifted to Quetta,” Bangulzai had told AFP earlier.
Balochistan’s Civil Defence Director Aslam Tareen, as well as Bangulzai, had both confirmed earlier that the blast was the result of a suicide attack.
Provincial officials said an unidentified attacker had targeted a corner meeting organised by Siraj, a Balochistan Awami Party (BAP) candidate for PB-35 (Mastung). Senior provincial official Saeed Jamali said the bomber detonated his explosives in the middle of the compound where the political meeting was taking place.
Senior Vice-President of BAP Sarfaraz Bugti condoled Nawabzada Siraj’s death.
It is pertinent to mention here that the spy chiefs of Russia, Iran, China and Pakistan had reportedly met on Tuesday in Islamabad over the growing threat to the region from the militant Islamic State in Afghanistan.
The Foreign Office had denied knowledge of the meeting, but officials had privately confirmed to Dawn that the meeting took place.
Earlier today, a blast targeted former Khyber Pakhtunkhwa chief minister Akram Khan Durrani’s convoy in Bannu. While Durrani remained safe, four people were killed and 32 others injured in the attack.
Last night, two people had been injured in a blast near BAP’s election office in Khuzdar.
On July 10, a suicide blast had killed Awami National Party (ANP) leader Haroon Bilour and 19 others in Peshawar’s Yaktoot area. The attack was claimed by the Tehreek-i-Taliban Pakistan (TTP) which had also claimed responsibility for 2012 attack that killed Haroon’s father, Bashir Bilour.
On July 7, at least seven people, including a candidate of Muttahida Majlis-i-Amal (MMA), were injured when a convoy came under a bomb attack in Bannu.
Earlier this month, an attack on a Pakistan Tehreek-i-Insaf (PTI) candidate’s office in North Waziristan’s Razmak tehsil had injured 10.
Following the attacks, activists called for authorities to remain vigilant to protect candidates during the final days of the campaign season.
“The Pakistani authorities have a duty to protect the rights of all Pakistanis during this election period ─ their physical security and their ability to express their political views freely, regardless of which party they belong to,” said Omar Waraich, deputy South Asia director at Amnesty International.
The Election Commission of Pakistan has also sought a detailed briefing from the National Counterterrorism Authority (Nacta) on the threats faced by politicians and candidates.
In May 2017, 28 people were killed and over 40 others injured in an explosion near a local seminary in Mastung, which targeted the convoy of then deputy chairman Senate Abdul Ghafoor Haideri.
In 2014, more than two dozen people were killed and several injured when a powerful explosion ripped through a bus carrying Shia pilgrims.
In 2012, 19 people were killed and 25 others injured after three passenger buses were struck by an explosion in Mastung’s Dringarh area. A remotely-triggered bomb had hit a convoy of three buses and set one of them ablaze.