Kano - The death toll has risen to 49 after a suicide bomber disguised in a school uniform blew himself up at a boys' secondary school in Yobe State on Monday, national television reported.
The report said 57 people were injured. Other reports put the number of injured victims at 79 in the attack in Potiskum, Yobe state, which took place as students were in the yard of the boarding school during the morning roll call.
Police Commissioner Markus Danladi said the exact number of casualties could not be confirmed until he had reached the site, which is about 120km from the state capital, Damaturu.
One parent, Mahe Ibrahim, told dpa that a teacher at the school confirmed 30 deaths when he called to enquire about his child.
"I just finished speaking to the house master of my boy and he said about 30 bodies have been evacuated by the ambulance. Though my child is safe, I greatly feel for the parents of the casualties," he said.
"About 15 students, whose bodies were disfigured but still bleeding at the scene of the explosion, died on the way to the general hospital," volunteer helper Ahmed Yunus told the online newspaper The Daily Trust.
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The Daily Trust quoted local resident Kulu Mustapha as saying the bomber had "disguised [himself] as a student because he wore the same uniform being used by students of the school."
"I can tell you all schools in the town have been closed now as parents have gone to pick up their children. There is wailing everywhere, especially around the school where the incident happened," local resident Ibrahim Ahmed told the publication The Punch.
The attack came six days after a similar one on a Shi'ite Islamic school in Potiskum, in which about 30 people died.
According to reports, both attacks are suspected to be the work of the radical Islamist group Boko Haram, which had already targeted schools in an attempt to prevent children from getting a Western education.
Boko Haram has killed thousands of people during its five-year campaign to establish an Islamist state.
The United Nations and United States strongly condemned the bombing.
UN Secretary General Ban Ki-moon noted the frequency and brutality of attacks against schools in the region and called for an immediate end to these "abominable crimes," said Farhan Haq, Ban's spokesperson.
The UN Children's Fund (Unicef) said attacks on children are attacks "on the future of Nigeria" warning that the country already has the largest number of children out of school in the world.
The United States urged the government of Nigeria to "investigate these and other attacks to bring the perpetrators to justice," said State Department spokesperson Jen Psaki.