A suicide bomber dressed as a student killed at least 48 people, most of them students, and injured 79 others at a school assembly in the northeastern Nigerian town of Potiskum on Monday, a hospital official said.

No one immediately claimed responsibility for the attack in Yobe State, a territory close to the stronghold of Boko Haram Sunni Muslim militants, who have staged a five-year insurgency.

Boko Haram, which is Hausa for "Western education is sinful", has attacked schools, abducted hundreds of students and killed thousands in its fight for an Islamist state, and is seen as the main security threat to Africa's leading oil producer.

"So far, the number of the dead is 48, while 79 are injured. I counted the bodies, mostly students and a few teachers," 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," she said, asking to remain anonymous.

Mariam Ibrahim, a teacher at the Government Science Secondary School (GSS) in Potiskum told Reuters the bomb went off as she was arriving and students were at morning assembly.

Potiskum resident Aliyu Abubakar said he heard the explosion when he was dropping off his two sons at a nearbyIslamic college. "One of my sons fell down, I came out dragged him in and we drove off back home," he said.

A second teacher, asking to remain anonymous, said, "There are some (others) that are critically injured and I am sure the death toll will rise."

Boko Haram has intensified its attacks in the past few weeks since a purported ceasefire agreement, announced by the Nigerian government, was later rejected by the group's leader in a video.

(Reuters)