The rights group Amnesty International says hundreds of people are dying in military detention as Nigeria's security forces crack down on an Islamist uprising in the country's northeast.
More than 3,600 people are said to have died in the Boko Haram conflict, including killings by the security forces
Amnesty International said more than 950 people died in military custody in the first six months of this year, according to "credible information" from a senior Nigerian army officer.
If true, that would mean that Nigeria's military has killed more civilians than the extremists during the first half of 2013.
Amnesty International said all those killed were detained as suspected members or associates of the Boko Haram terrorist network that has claimed responsibility for attacks that have killed hundreds of Muslim and Christian civilians this year in their mission to overturn democracy and force Nigeria to become an Islamic state.
In a new report that includes testimony from freed detainees, Amnesty International said some detainees had been shot outright, some starved and others suffocated to death in overcrowded cells.
"People suspected of being Boko Haram members are arrested, they are shot in the leg during interrogation, and they are left to bleed and some of them bleed to death," Amnesty International West Africa researcher Makmid Kamara told DW.
"No visible gunshot wounds"
Most deaths recorded by the rights group took place at the Presidential Lodge guardroom and a detention center in Damaturu, and at Giwa Military Barracks in Maiduguri, the capital of Borno state and the birthplace of Boko Haram.
"I've been going to Nigeria to do my research and I have seen bodies dumped outside mortuaries, the state's specialist mortuary in Maiduguri, for example," Kamara said.
A state of emergency was declared in the three Nigerian states hardest hit by Boko Haram in May 2013
He said that he had counted some of those bodies, which eye-witnesses said had been deposited by the Joint Task Force, the Nigerian military. "They didn't have any visible gunshot wounds and we found out later that they had starved to death," he said.
Kamara also said that former detainees had told Amnesty that "when colleague detainees die and they are not taken out of the cells, they use the dead corpses in the cells as pillows."
Human rights activist Shehu Sani of the northern-based Nigerian Civil Rights Congress said he believes thousands have been detained, the news agency AP reported from Lagos.
Letter sent to the Nigerian authorities
Amnesty said it was very aware that the Nigerian government has a responsibility to protect the citizens of Nigeria from attacks and human rights abuses by non-state actors, but the Nigerian authorities should abide by international human rights standards when carrying out those responsibilities.
"We think these allegations of deaths in military custody flout all international human rights standards," Kamara said.
Amnesty wants an immediate probe into the allegations.
Kamara said the rights group had sent a letter to officials at the Nigerian defense headquarters in Abuja in September, highlighting concerns they had raised previously in a meeting with them, but there hadn't been any response.