The death toll from the powerful suicide bombing at a political convention of a hardline Islamist party in Pakistan's restive Khyber Pakhtunkhwa province sharply rose to 54 on Monday, police said as they intensified efforts to hunt down those behind the massive attack.

Police also said that an initial probe has suggested that the banned terrorist group ISIS is behind the suicide attack that injured over 100 people in Khar, the capital of Bajaur tribal district.

The local branch of ISIS has previously targeted JUI-F party leaders as they consider them apostates.

The attack took place on Sunday when more than 400 members of the conservative Jamiat Ulema Islam-Fazl (JUI-F) party, known for its links to hardline political Islam, had gathered for a meeting under a large tent in the town of Khar, which borders Afghanistan.

The JUI-F is a party that is part of the coalition government led by Pakistan Muslim League-Nawaz (PML-N). The major terror attack occurred as Pakistani political parties are beginning campaign preparations ahead of elections in the coming months.

Pakistan President Arif Alvi prayed for eternal peace for the departed souls. He also wished speedy recovery for the injured and emphasised timely medical assistance to them.

In a statement issued on Sunday, Khyber Pakhtunkhwa caretaker Chief Minister Azam Khan sought a detailed report on the blast from police.

He also visited the Combined Military Hospital in Peshawar, where he met and inquired about the health of injured persons.

Rahim Shah, a witness, told Dawn.com that more than 500 people were attending the convention when the blast occurred.

"We were listening to a bayan [sermon] when a powerful explosion knocked me unconscious," he said. Shah narrated that when he regained consciousness, there was blood everywhere.

"People were screaming and even shots were fired," he added.

Sabeehullah, a 24-year-old JUI-F supporter who had his arm fractured by the blast, said the scale of injuries was horrifying.

"There was utter confusion, with human flesh, limbs, and body parts scattered throughout the area, alongside lifeless bodies. I found myself lying next to someone who had lost their limbs. The air was filled with the smell of human flesh," he was quoted as saying in the report.

The JUI-F chief, in a statement issued by the party's media cell, expressed grief over the incident. He sought an inquiry into the attack from Prime Minister Sharif and the KP government.

"May Allah raise the ranks of martyrs," Fazl said and prayed for the speedy recovery of the injured.

He also appealed to JUI-F workers to immediately reach hospitals and provide blood donations.

In a tweet, Interior Minister Rana Sanaullah vowed to bring the perpetrators of today's attack to justice.

"The cowardly acts of terrorists cannot dampen our spirits," he said.

Former prime minister Imran Khan said he was saddened to learn about the blast and extended condolences to the victims' families.

"The rise in terror incidents across Pakistan particularly in KP, calls for an urgent need to reconsider our priorities," he said, adding that the authorities should focus on eliminating terrorism.

Zabihullah Mujahid, a spokesman for the Taliban government in Afghanistan, has condemned the attack. TTP spokesman Khalid Khurrasani also condemned the blast.

Pakistan has witnessed a surge in terrorist attacks following the Taliban's return to power in Afghanistan in August 2021.

On January 30, a Pakistan Taliban suicide bomber blew himself up during the afternoon prayers in a mosque in Peshawar, killing 101 people and injuring more than 200 others.

In February, heavily armed TTP militants stormed the Karachi Police chief's office in Pakistan's most populous city, sparking gunfire that killed three rebels and four others, including two police constables.