The group Human Rights Watch is calling for an investigation into the death late Thursday of a radical Islamist leader.
Police in Nigeria have reacted sharply to reports that the leader of a Nigerian Islamist sect, Mohammed Yusuf, may have been a victim of extra judicial killing. Some reports say the militant leader was killed in police custody, but the police say he died in a shootout with security forces at his headquarters in the city of Maiduguri.
Hundreds of people were killed in five days of clashes involving Muslim rebels with a group called Boko Haram and government forces.
Militants seeking to impose Islamic law throughout Africa's most populous nation had attacked security forces in a wave of violence that started on Sunday in Bauchi, and quickly spread to three other states in Muslim-dominated northern Nigeria.
The governor of Bauchi state, Issa Yuguda, said he was overwhelmed by the arms and ammunition at the disposal of the group.
"They had all sorts of ammunitions that were unbelievable. You won't believe such caliber of people will have such ammunitions, including rocket launchers. If you see the kinds of explosives they have, the kind of guns they have, the kind of bow and arrows they have, the kind of knives they use, you will be scared," he said.
President Umaru Yar'Adua had ordered security forces to take all necessary action to contain and repel attacks by the extremists.
An official of the State Security Service, Naralyn Ogar, dismissed suggestions that the Boko Haram was affiliated with international terrorist groups.
"As far as we are concerned, they are religious fundamentalists, and they will remain so. They call themselves self-styled Nigerian Taliban, they have nothing to do with outside. They just want to assume the stance in order to create the impression that they have backings from outside," said Ogar
Calls for a full-scale investigation into the government's handling of the crisis are expected to grow in the coming days and weeks following reports of heavy-handedness by security agents and the high number of civilian casualties.