DAMATURU, Nigeria — A suicide bomber dressed as a student killed at least 48 people at a school assembly in northeastern Nigeria on Monday, a hospital official said. Most of the victims were students. No one immediately claimed responsibility for the attack in the town of Potiskum in Yobe State, a territory that has been hit by Islamist Boko Haram rebels during a five-year insurgency. “So far, the number of the dead is 48, while 79 are injured,” a nurse at Potiskum General Hospital told Reuters. “A teacher who survived the blast with minor injury said the bomber dressed like a student and was also on the assembly ground with the students.”Asking to remain anonymous, one teacher said: “There are some [others] that are critically injured and I am sure the death toll will rise.” Boko Haram, whose name means “Western education is sinful” in the local Hausa language, has targeted schools, abducted students and killed thousands in its campaign to carve out an Islamist state.