The blast targeted the Jamiat Ulema-e-Islam-F (JUI-F) party -- a government coalition partner led by an influential firebrand cleric -- as hundreds of supporters of hard-line Pakistani cleric and political party leader Fazlur Rehman congregated under a canopy in the town of Khar, in Bajur district.
The Bajur district near the Afghan border was a stronghold of the Pakistani Taliban — a close ally of Afghanistan’s Taliban government — before the Pakistani army drove the militants out of the area.
Party officials said Rehman was not at the rally but organizers added tents because so many supporters showed up, and party volunteers with batons were helping control the crowd.
Officials were announcing the arrival of Abdul Rasheed, a leader of the Jamiat Ulema Islam party, when the bomb went off in one of Pakistan’s bloodiest attacks in recent years.
"The tent had collapsed on one side, trapping people who were desperately attempting to escape," said Abdullah Khan, who tried to help the victims.
"There was utter confusion, with human flesh, limbs, and body parts scattered throughout the area, alongside lifeless bodies."
Sabeeh Ullah, a 24-year-old party supporter who had his arm fractured by the blast, said the scale of injuries was horrifying.
"I found myself lying next to someone who had lost their limbs. The air was filled with the smell of human flesh," he told AFP by phone.
As the toll kept rising, Riaz Anwar -- the health minister for Khyber Pakhtunkhwa province -- told AFP late Sunday 44 people had been confirmed killed and over 100 wounded.
"It was a suicide attack, with the bomber detonating himself in close proximity to the stage," he told AFP.
Pakistani media said there were some 400 people in the tent at the time of the explosion, and that multiple emergency crews were working the scene.
Images from the blast site circulating on social media showed bodies strewn around, and volunteers helping blood-soaked victims to ambulances.
Pakistan's national assembly is due to dissolve in the next few weeks ahead of elections expected in October or November, and political parties are already preparing to campaign.
The blast coincides with a visit to the country by a senior delegation of Chinese officials, including Vice Premier He Lifeng, who arrived in the capital Sunday evening.
Pakistani Prime Minister Shehbaz Sharif condemned the blast Sunday on social media, offering condolences to the victims and vowing to punish those responsible.
Local Islamic State active
Provincial police said in a statement that the attack was carried out by a suicide bomber who detonated his explosives vest close to the stage where several senior leaders of the party were sitting.
It said initial investigations suggested the Islamic State (IS) group — which operates in Afghanistan and is an enemy of the Afghan Taliban — could be behind the attack, and officers were still investigating.
No group has claimed responsibility for the attack, but the local chapter of the IS has recently carried out attacks against JUI-F.
Last year, IS said it was behind violent attacks against religious scholars affiliated with the party, which has a huge network of mosques and madrassas in the north and west of the country.
The jihadist group accuses JUI-F of hypocrisy for being an Islamic group while supporting hostile governments and the military.
The party's leader, Fazlur Rehman, started political life as a firebrand Islamist hardliner but has softened his public image over the years in a bid to forge alliances with secular parties on the left and right.
With the ability to mobilise tens of thousands of madrassa students, his party never musters enough support for power on its own, but is usually a key player in any coalition.
Pakistan's home-grown Taliban group, Tehreek-e-Taliban Pakistan (TTP), which largely directed its campaign against security officials, said in a statement sent to The Associated Press that the bombing was aimed at setting Islamists against each other.
Zabiullah Mujahid, a spokesman for the Afghan Taliban, said on the social media platform X, formerly known as Twitter, that “such crimes cannot be justified in any way.”
The Afghan Taliban’s seizure of power in Afghanistan in mid-August 2021 emboldened the TTP. They unilaterally ended a cease-fire agreement with the Pakistani government in November, and have stepped up attacks across the country.
In January, a suicide bomber linked to Pakistan's Taliban blew himself up in a mosque inside a police compound in the northwestern city of Peshawar, killing more than 80 officers.
The militant assaults have been focused in regions abutting Afghanistan, and Islamabad alleges some are being planned on Afghan soil -- a charge Kabul denies.
Pakistan was once plagued by almost daily bombings, but a major military clearance operation in the former tribal areas starting in 2014 largely restored order.
The seven remote districts that border Afghanistan, of which Bajaur is one, were later brought under the control of Pakistani authorities after the passage of legislation in 2018.
Analysts say militants in the former tribal areas have become emboldened since the return of the Afghan Taliban.
One security analyst suggested Sunday's attack was more likely linked to the election rather than having a sectarian motive.
"This is part of terrorism violence that seems to be ramping up in Pakistan ahead of elections to create a sense of instability that could eventually lead to a delay in the elections," said Imtiaz Gul, executive director of the Center for Research and Security Studies.