[caption id="attachment_1126" align="alignleft" width="820"] Some of the wounded were taken in critical condition to the main hospital in Khar, Pakistan [Rescue 1122 Head Quarters/AP][/caption] An explosion that occurred in Pakistan during a rally organized by an Islamist party claimed at least 37 lives. The explosion in the northwest Bajaur area, where Jamiat Ulema-e-Islam-Fazl (JUI-F) was having a meeting, also injured more than 100 people. The BBC was informed by police that they had discovered evidence suggesting that the explosion may have been a suicide strike. All injured people have been transferred to hospitals after the rescue effort was finished, according to the police. 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 Sharifcondemned 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.