Abuja (AFP) - Nigeria's president-elect Muhammadu Buhari on Monday denounced Boko Haram's claim to be a religious group, slamming its attacks on civilians and vowing a hard line against the Islamist militants.

"The fraud called Boko Haram can be defeated by denying it a recruitment base. No religion allows for the killing of children in school dormitories, in markets and places of worship," he said.

"They have nothing to do with religion. They are terrorists and we are going to deal with them as we deal with terrorists."

Buhari, 72, won presidential elections last month with a promise of a tough stance against Boko Haram, whose insurgency has killed at least 15,000 since 2009 and left more than 1.5 million homeless.

The former military ruler accused his opponent President Goodluck Jonathan of a failure of leadership in tackling the security threat.

On Jonathan's watch, Book Haram kidnapped more than 200 schoolgirls from their home town of Chibok in the northeastern state of Borno. More than a year on, 219 are still being held.

"The worst thing anybody can do is to deny children access to education," Buhari said in a statement issued by his All Progressives Congress (APC) party.

"That will be destructive to their lives and we are not going to allow that to happen."

Buhari, who takes office on May 29, has cautioned he cannot make promises to return the kidnapped schoolgirls.

But he has pledged to help areas hit by the violence -- as well as years of social and economic deprivation -- with development programmes to prevent radicalisation.