Earlier in the day, at least four people were killed and 16 injured in a bomb attack on a campaign motorcade of a political party in Khyber Pakhtunkhwa Province in northwestern Pakistan, hospital and administration officials said.
Mr Raisani was killed when a suicide bomber blew himself up at a rally amid scores of supporters. Siraj's death was confirmed by his brother Lashkari Raisani.
The United States has strongly condemned the attacks on Pakistani political candidates and their supporters.
"These attacks are cowardly attempts to deprive the Pakistani people of their democratic rights", it said.
Raisani was the younger brother of former provincial chief minister Mir Aslam Raisani.
Durrani was unhurt in the attack.
Balochistan government has also announced two-day mourning in the province over the tragic suicide bomb blast in Mastung on Friday, in which one hundred twenty-eight people were martyred and around two hundred others injured.
It said the national flag will fly at half-mast tomorrow to mourn the deaths of almost 150 people in the recent terrorist strikes ahead of the July 25 general elections.
This is the third attack this week on a target related to the upcoming election.
Raisani, who was a candidate from PB-35 (Mastung), was among those killed in the attack.
The Islamic State-claimed suicide attack in the town of Mastung, near the Balochistan provincial capital Quetta, was the latest in a series of bombings targeting campaign events in the last week, sparking fears of more violence ahead of nationwide polls on July 25.
Pakistan's caretaker government launched a crackdown on political gatherings on Friday as Sharif, who was ousted by the Supreme Court previous year and convicted in absentia of corruption a week ago, flew back to rally his party ahead of the general elections.
"We have imposed emergency (management) in the hospitals and cancelled the vacations of the doctors and paramedics", Balochistan home minister Agha Umar Bungalzai told AFP.
It comes amid news a plane carrying disgraced former Prime Minister Nawaz Sharif and his daughter Maryam Nawaz landed at Allama Iqbal International Airport in the eastern city of Lahore.
Sharif's son-in-law is now serving a one-year prison sentence on the same charge, which stems from the purchase of luxury apartments in Britain that the court said were bought with illegally acquired money. "The security institutions should work on this", he said.
Pakistan's army will deploy about 371,000 troops on election day, nearly three times the number in 2013, to protect the polling places.
Earlier this week, a suicide blast had killed Awami National Party leader Haroon Bilour and 19 others in Peshawar.
The NACTA had recently warned of possible deadly attacks on various politicians, including Imran Khan, ANP's head Afsandyar Wali, chairman of the Qaumi Watan Party (QWP) Aftab Ahmad Khan Sherpao and some PML-N leaders.
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