TEHRAN, Young Journalists Club (YJC) - "Twenty people were killed in the blast and we fear this toll may rise," Agha Umar Bungalzai, provincial home minister, told AFP on Friday.
He added that more than 40 people were also injured in Mastung town, near the provincial capital of Quetta.
The official confirmed that the blast also killed Siraj Raisani, younger brother of former provincial chief minister Mir Aslam, who was running for a provincial assembly seat with Balochistan Awami Party (BAP).
"Mir Siraj Raisani succumbed to wounds while he was being shifted to Quetta," Bungalzai said.
Pakistan's caretaker government launched a crackdown on political gatherings on Friday after former Prime Minister Nawaz Sharif returned home to rally his party ahead of the general elections.
The National Accountability Bureau (NAB) court on July 6 handed down a 10-year jail term to Sharif in a corruption case linked to his family's purchase of upscale flats in London.
The anti-corruption court accused the Sharif family of failing to prove a legal source of income for the purchase of Avenfield apartments in London in the mid-1990s.
Earlier on Friday, four people were killed and 39 injured after a bomb hidden inside a motorcycle detonated near the campaign of a Pakistani politician in the country's northwest town of Bannu near the Afghan border.
According to Pakistani police, the blast hit the convoy of the Muttahida Majlis-e-Amal (MMA) candidate Akram Khan Durrani, who survived the attack.
At least 22 people were killed in a bombing attack on an anti-Taliban political event held in northwestern Pakistan on July 10.
The blast targeted a campaign event held in the city of Peshawar organized by the Awami National Party (ANP), which has been targeted in the past over its opposition to militant groups such as the Taliban.
Late in May, Pakistan's President Mamnoon Hussain approved July 25 as the date for general elections that is likely to result in a change of government.
Pakistan’s current government, led by Prime Minister Shahid Khaqan Abbasi, and parliament are due to end their terms on May 31, when an interim government would be formed to handle state affairs until the elections.
The ruling Pakistan Muslim League-Nawaz (PML-N) and the main opposition party, Tehreek-e-Insaf (PTI), will be the main contenders in the vote.
Political wrangling between the two parties in parliament had resulted in a delayed announcement of an interim government.
Abbasi on May 28 appointed former chief justice Nasir-ul-Mulk as caretaker prime minister until general elections.
The incumbent prime minister told reporters that parties had agreed on a candidate who "no one can object to" and added, “No Pakistani can lift a finger (against) such a name.”