At least 133 people, including a top nationalist leader, were killed and over 200 others injured on Friday in a powerful suicide blast and a targeted attack on separate election rallies in Pakistan, the deadliest in a series of assaults on candidates ahead of the July 25 polls.
"Raisani succumbed to wounds while he was being shifted to Quetta," District Police Officer Mohammad Ayub Achakzai said.
Raisani is the brother of former Chief Minister of Balochistan Nawab Aslam Raisani.
The Islamic State terror group has claimed responsibility for the attack, police officials said.
The outfit announced the claim through its Aamaq news agency without providing further details.
Local media confirmed the death toll, quoting Balochistan's Home Minister Agha Umar Bangalzai.
"We have more than 200 people injured and under treatment at different hospitals in Quetta and condition of some of the wounded is critical," he said.
"Initially the death toll was not high but many critically injured persons including Siraj Raisani passed away in hospitals," Balochistan's caretaker health minister Faiz Kakar said.
Officials of the Bomb Disposal Squad (BDS) confirmed that it was a suicide blast. They said that around 16-20 kilogram of explosives were used in the attack.
Following the incident, an emergency was declared in Quetta hospitals, with additional medical staff summoned.
The attack came hours after a bomb hit a rally of Akram Khan Durrani of Mutahida Majlis Amal (MMA), an alliance of religious party, including Jamiat Ulema-e-Islam-Fazal (JUI-F) and Jamaat-e-Islami, in Bannu area of Khyber-Pakhtunkhwa province.
Durrani was unhurt in the attack. He later visited the injured in a hospital in Bannu and said that his vehicle was damaged in the attack.
Durrani, who is contesting in July 25 elections against Pakistan Tehreek-e-Insaaf chief Imran Khan, announced that he will continue campaign despite threats.
The twin attacks came as former prime minister Nawaz Sharif along with his daughter Maryam returned to the country to face arrest in a corruption case.
The law and order had suddenly deteriorated ahead of elections despite claims by the government and security forces that terrorism has been wiped out of the country.
President Mamnoon Hussain and Prime Minister Nasirul Mulk also condemned the attack in separate statements.
The Pakistan Tehreek-e-Taliban claimed responsibility for the attack on the ANP rally.
On July 7, seven people were injured when a convoy of a Muttahida Majlis-i-Amal came under attack in Bannu.