An explosion at a religious gathering in Pakistan’s northwestern Swat valley that killed 22 people and wounded more than 80 was caused by a bomb, officials said on Friday. The explosion took place at a weekly meeting of the local Tableeghi Jamaat (preachers’ party) at its centre on the outskirts of Mingora, the main town in the district, on Thursday. It was the deadliest blast in Swat since the Pakistan army declared it back under government control in July 2009 following a two-year Taliban-led insurgency in the valley. “The explosion occurred due to a bomb. Around five kilograms (11 pounds) of explosives were used in the blast,” Shafqat Malik, a senior bomb disposal official in Peshawar, told AFP. Initial reports had said the blast was due to a gas cylinder exploding and that no trace of explosives had been found at the site. Regional police chief Akhtar Hayat said that a joint investigation by police and the army was under way. “It was a terrorism incident, we are investigating further details,” he told AFP. Local administration chief Kamran Khan told reporters earlier at the Tableeghi centre that 22 people had been killed and 87 wounded, 20 of whom were in serious condition. Police officer Gul Afzal Afridi confirmed the casualty figures. There were around 1,500 people listening to a Muslim cleric give a speech at the centre when the blast occurred, he said. Tableeghi Jamaat is a non political organisation and attacks on its gatherings are very rare. Internationally renowned Pakistani school girl campaigner Malala Yousafzai was shot in the head in Mingora last October in an attack claimed by the Pakistani Taliban. She is now recovering in Britain. The Pakistani Taliban seized much of Swat during a 2007-2009 insurgency but the army declared the region back under its control after an offensive in July 2009.