At least 44 people have been killed in an explosion in Pakistan during a rally organised by an Islamist party.
More than 100 people were also injured in the explosion in north-west Bajaur district, where Jamiat Ulema-e-Islam-Fazl (JUI-F) was holding a meeting.
Police told the BBC that they have found evidence suggesting the explosion was a possible suicide attack.
A rescue operation has been completed and all injured have been taken to hospital, officers said.
Officials have warned the death toll may rise further, as 15 people are in a critical condition.
The motivation behind the attack is not yet clear. Security forces have cordoned off the area and an investigation into the explosion is taking place.
Hundreds of people were attending the JUI-F workers' convention on Sunday in the town of Khar, in the Pakistani tribal district of Bajaur, Khyber Pakhtunkhwa province, near the border with Afghanistan.
Pictures showed hundreds of people gathered under a canopy when the blast happened close to the stage.
One eyewitness said the tent collapsed, trapping people who were desperately trying to escape.
Images broadcast on local TV show ambulances ferrying injured people to hospital, while police confirmed those with serious injuries have been flown by military helicopters to nearby Peshawar for urgent medical treatment.
Authorities have declared a health emergency at the district hospital.
Some badly injured people have been waiting in the hallways of health clinics struggling to cope with the high number of casualties.
A regional leader of the JUI-F, Maulana Ziaullah, was killed in the blast, local officials told the BBC.
JUI-F is a major religious political party and forms part of the government coalition in Pakistan's parliament.
Pakistan's Prime Minister Shehbaz Sharif condemned those responsible as being terrorists who have "targeted those who speak for Islam, the Quran and Pakistan" and said they would face "real punishment".
"The terrorists are enemies of Pakistan, we will eliminate them from the face of existence," the PM said in a statement.
The political gathering was an opportunity for the JUI-F to rally its support, ahead of an election expected to take place later this year.
While no-one has yet said they carried out the attack, the local branch of Islamic State group (IS) in Pakistan claimed to be behind several attacks this year in Bajaur and has previously claimed targeting JUI-F.
In June, the militants said they were behind the assassination of a party official in the village of Inayat Killi.
IS issued the claim in the name of its "Khorasan Province" branch (ISKP), which operates in Afghanistan and north-west Pakistan. The group also claims attacks in Pakistan in the name of its "Pakistan Province" branch.
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