Police in Myanmar said they were investigating the head of a mosque and a Muslim teacher for possible negligence after a fire swept a religious dormitory yesterday, killing 13 children in a blaze that raised new concern over sectarian tensions. Authorities blamed the fire on an electrical short circuit and deployed riot police to maintain calm. But some Muslims remained suspicious, saying it was set intentionally. Myanmar has been on edge after sectarian unrest between Buddhists and Muslims erupted in the central city of Meikhtila last month, killing dozens of people and displacing more than 12,000, mostly Muslims. The violence has since spread to other towns where Buddhist mobs have torched or ransacked mosques and Muslim-owned property. Police officer Thet Lwin said about 75 children lived in the torched compound in eastern Yangon - which encompasses a mosque, a school and a dormitory - and most were able to escape by running out of a door rescue workers knocked open. Security bars blocked most of the building's windows. Mosque member Soe Myint said most of the children, who had been sent to the religious boarding school by their parents, were sleeping on the ground floor when the blaze began and were able to flee. But 16 were sleeping in a small loft and were trapped when the stairs to it caught fire. Three boys jumped to safety and the rest died, he said. Soe Myint said he did not believe the fire was caused by a short circuit and urged authorities to launch an investigation. "The whole mosque smelled of diesel," he said. "We don't use diesel at the school." Yangon Division Chief Minister Myint Swe later said police discovered a diesel container underneath a staircase. He said the fuel was normally used to power a mosque generator when the electricity is out. Hla Myint, whose 15-year-old nephew died in the blaze, waited in a crowd outside Yangon General Hospital, where the dead were taken. Two trucks of riot police were parked nearby. "We sent him to school only yesterday and today he is dead," she said. "We are so sad we can't express it." Later yesterday, several thousand mourners gathered at a cemetery on the outskirts of Yangon for a group burial. US Ambassador Derek Mitchell issued a statement saying he was "deeply saddened" by the deaths. He also called on the government to "conduct a thorough and transparent investigation into the cause". Authorities were investigating the head of the mosque and a teacher, but no arrests had been made, said city Police Chief Win Naing. "As the two people in charge, they are responsible for this and we have to take action against them," he said. Win Naing said the fire started in a voltage regulator under the stairs that led to the sleeping loft and that firefighters had to break two locks on the door of the mosque to rescue the survivors. He ruled out arson, saying that three police were guarding the mosque and saw no one approach the building before the fire started. Earlier Thet Lwin, the policeman, blamed the fire on an electrical short circuit "and not due to any criminal activity". Every time he mentioned the word "electrical short," though, angry Muslims shouted and began banging on vehicles with their fists. Zaw Min Htun, a member of a local Muslim youth organisation, said he entered the charred building and also smelled fuel. "Muslims are very angry," he said. "The children are innocent. ... Someone burned the mosque."