Pakistan held funerals on Monday for victims of a suicide bombing that targeted a rally of a pro-Taliban cleric the previous day as the death toll climbed to at least 45 and the government vowed to hunt down those behind the attack.

No one immediately claimed responsibility for Sunday's bombing, which also wounded 200 people. Police said their initial investigation suggested the Isis group's regional affiliate could be behind the attack.

The victims were all from the Jamiat Ulema Islam party, led by cleric and politician Fazlur Rehman.

He didn’t attend the rally, held under a large tent close to a market in Bajur, a district in the Khyber Pakhtunkhwa province that borders Afghanistan.

The Isis regional affiliate – known as the Islamic State in Khorasan Province – is based in neighbouring Afghanistan's Nangarhar province and is a rival of the Afghan Taliban. Bajur was a stronghold of the Pakistani Taliban – a close ally of Afghanistan’s Taliban government – before several Pakistani army offensives that ended in 2016 claimed to have driven them out of the area.

The cleric's supporters had gathered in Bajut on Sunday as part of their party's preparations for the next election, expected sometime in October or November after the current parliament's five-year term ends.

Prime minister Shehbaz Sharif is expected to dissolve the parliament in August to pave the way for the vote. Mr Rehman’s party is part of Sharif’s coalition government, which came to power in April 2022 by ousting former prime minister Imran Khan through a no-confidence vote in the legislature.

Mr Khan later on Sunday condemned the bombing as condolences continued to pour in from across the country.

Dozens of people who received minor injuries were discharged from hospital while the critically wounded were taken to the city of Peshawar by army helicopters.

The death toll on Sunday was reported to be 44 but rose to 45 on Monday as a critically wounded person died at a hospital, physician Gul Naseeb said.

Mr Sharif called Mr Rehman to express his condolences and assure the cleric that those who orchestrated the attack would be punished.

The bombing drew nationwide condemnation, with ruling and opposition parties offering condolences to the families of the victims. The US and Russian embassies in Islamabad also condemned the attack.

Abdul Rasheed, a senior leader in Mr Rehman's party, said the bombing was aimed at weakening the party but that “such attacks cannot deter our resolve”.

The Pakistani Taliban also distanced themselves from the attack. The outlawed Tehreek-e-Taliban Pakistan, or TTP, said the attack aimed to set Islamists against each other. Zabihullah Mujahid, the spokesman for the Afghan Taliban, posted on X that “such crimes cannot be justified in any way”.

The bombing came hours before the arrival of Chinese vice premier He Lifeng in Islamabad, where on Monday he was to participate in an event to mark a decade of the China-Pakistan Economic Corridor.

The corridor is a sprawling package under which Beijing has invested billions of dollars in Pakistan.

In recent months, China has helped Pakistan avoid a default on sovereign payments. Some Chinese nationals have also been targeted by militants in northwestern Pakistan and elsewhere.

Feroz Jamal, the provincial information minister, said that police were "investigating this attack in all aspects”.

Sunday's bombing was one of the four worst attacks in northwestern Pakistan since 2014, when 147 people, mostly schoolchildren, were killed in a Taliban attack on an army-run school in Peshawar.

In January, 74 people were killed in a bombing at a mosque in Peshawar. In February, over 100 people, mostly policemen, died in a bombing at a mosque inside a high-security compound housing Peshawar police headquarters.