Nigeria's largest grouping of Christian churches on Friday condemned the killing of a female student who was beaten and burned by fellow students for alleged blasphemy and demanded the authorities bring the culprits to justice.

Two suspects were arrested in connection with the murder of Deborah Samuel, who was accused by other students of posting blasphemous statements about the Prophet Mohammad in a Whatsapp group. 

Nigeria is almost evenly divided between the largely Christian south and mainly Muslim north, where some states have adopted strict sharia laws, including death sentences for blasphemy.

The Christian Association of Nigeria (CAN), whose members include Catholic, Anglican and Methodist churches as well as indigenous churches, said those responsible for killing Samuel in the northwestern state of Sokoto should be prosecuted.

"The unlawful and dastardly action of the perpetrators must not only be condemned by all right thinking people but the security operatives must fish them out, prosecute them as it is expected of them," Joseph Daramola, CAN general secretary said.

Witnesses said school security and police attempted to rescue the victim but were overwhelmed by the students.

President Muhammadu Buhari said in a statement there should be an impartial investigation and criticised those who took the law into their own hands.

"Violence has and never will solve any problem," he said.

Showing the religious and political sensitivities of the case, former vice president and presidential aspirant Atiku Abubakar, a Muslim, deleted his Twitter post condemning the incident.

Nigerians go to the polls next year to elect a new president, governors and parliamentarians. Abubakar is seeking the opposition ticket to run for president for the sixth time.

Reuters has not been able to reach Samuel's family for comment.