A SUICIDE bomber dressed as a pupil has killed at least 48 people, most of them pupils, and injured 79 others at a secondary school assembly in the north-eastern Nigerian town of Potiskum.

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

Angry locals blocked access to the school and an adjoining hospital after the terror attack, preventing security forces from getting close to the site of the explosion.

People in the crowd, who threw stones and shouted at the troops, sought to avoid a repeat of the events last week when members of the security forces fired at residents after a bomb killed nearly 30 people, a police source said.

Locals were angry about the military's inability to halt a five-year Islamic insurgency that has killed thousands of people and driven hundreds of thousands from their homes.

Some 2,000 pupils had ­gathered for yesterday morning's weekly assembly at the Government ­Technical Science College when the explosion blasted through the school hall.

A nurse at Potiskum General Hospital said: "So far, the number of the dead is 48, while 79 are injured. I counted the bodies, mostly students and a few teachers."

"A teacher who survived the blast with minor injuries said the bomber dressed like a student and was also on the assembly ground with the students."

Police confirmed the bomber was disguised as a pupil.

Mariam Ibrahim, a teacher at the school in Potiskum, said the bomb went off as she was arriving and pupils were at morning assembly.

Pupils Musa Ibrahim Yahaya, 17, said: "We were waiting for the principal to address us, around 7.30am, when we heard a deafening sound and I was blown off my feet. People started screaming and running, I saw blood all over my body." She is being treated for head wounds in hospital.

Survivors said the bomber appeared to have hidden the explosives in a type of rucksack popular with pupils.

Months ago, Nigeria's military reported finding a bomb factory where explosives were being sewn into rucksacks in the northern city of Kano.

Potiskum resident Aliyu ­Abubakar said he heard the ­explosion when he was dropping off his two sons at a nearby Islamic college.

He said "One of my sons fell down, I came out dragged him in and we drove off back home."

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 since the Nigerian government announced a ceasefire agreement last month as well as the imminent release of more than 200 school girls kidnapped by the group.

Boko Haram's leader denied a ceasefire deal had been reached and the schoolgirls have not been set free.

The group, whose name means "Western education is sinful" in the Hausa language, has attacked schools, abducted hundreds of pupils and killed thousands in its fight for an Islamist state

The terror group is seen as the main security threat to Africa's leading oil producer.