Police said they believed the attack may have been a suicide bombing. Pakistan's Information Minister Sheikh Rashid Ahmed told the AP agency: "This is the work of the The BBC's Zaffar Abbas in Islamabad says the blast took place in the centre of the prayer hall, causing chaos. Police said the bomb left a two-foot deep crater with the dead and wounded strewn across the floor. The police chief of Sialkot, Nisar Ahmed, told AP: "Dozens of people have been taken to hospital in critical condition and I think the casualties and death toll will rise." Police said a mob went on the rampage after the explosion, throwing stones at officers and attacking property. Our correspondent says police tried to push back the crowd to allow the wounded to be taken to hospital. At least 20 people were killed in a suicide bombing on a Shia mosque in Karachi in May. That attack followed the killing of a leading Sunni cleric.