Hundreds of people are dying in military detention as Nigeria's security forces crack down on an Islamic uprising in the northeast, Amnesty International said Tuesday. Some people are shot outright, some starve and others suffocate to death, it said.

"Others were reportedly shot in the leg during interrogations, provided no medical care and left to bleed to death," the London-based human rights group said in a new report that includes testimony from freed detainees.

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, it said. If true, that would mean that Nigeria's military has killed more civilians than the extremists during the first half of 2013.

Amnesty International called for an urgent investigation. But Nigeria's security forces are notorious for extrajudicial killings, according to rights groups and witnesses.

Two military spokesmen did not immediately respond to emails and phone calls seeking comment Tuesday, a public holiday as Muslims celebrate the feast of Eid al-Adha.

The killings and deaths documented by Amnesty International may help answer questions raised by an Associated Press report in August that detailed how hundreds of detainees have gone missing since the government imposed a state of emergency May 14 on three northeastern states that cover one-sixth of Nigeria.

The AP report said hundreds of people were being rounded up, often indiscriminately, in night raids. It said distraught relatives, human rights organizations and journalists have asked the army, the police, intelligence services and government officials where the arrested people are, but answers have not been provided.

Human rights activist Shehu Sani of the northern-based Nigerian Civil Rights Congress said he believes thousands are detained.

In an atmosphere of deep suspicion and fear, it is easy for people to settle personal grudges by identifying someone as a suspected terrorist.

Amnesty International said those killed all 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. This West African nation, Africa's biggest oil producer and most populous of some 160 million people, is almost equally divided between the predominantly Muslim north and mainly Christian south.

Most deaths recorded by Amnesty 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.

An AP reporter who was in Maiduguri saw military ambulances arriving at the mortuary of the main hospital in Maiduguri on an almost daily basis.

"Hundreds have been killed in detention either by shooting them or by suffocation. People are crammed into one cell. There are times when people are brought out on a daily basis and killed," Amnesty International quoted a second senior army officer as saying.

It said Amnesty International delegates in Maiduguri in April counted about 20 corpses on the ground outside the state hospital mortuary. "There were no visible gunshot wounds on the bodies. They looked emaciated." Witnesses told the group that the bodies were deposited by security forces.

It said several different sources said that when the mortuary is filled, bodies are taken away by the Borno State Environmental Protection Agency and buried in the cemetery.

"This is a staggeringly high figure that requires urgent action by the Nigerian government," said Lucy Freeman, Amnesty's deputy Africa director. "The details of what happens behind locked doors in these shadowy detention facilities must be exposed, and those responsible for any human rights violations brought to book."

Local and international human rights activists warned when thousands of troops were deployed in May that abuses by the military could help fuel the rebellion.

Civilians in northeast Nigeria and refugees among more than 30,000 who have fled to Cameroon, Chad and Niger have told AP reporters that they fear Nigeria's military as much as they do Boko Haram. They described soldiers attacked by the militants as avenging themselves on civilians.

In one of the worst cases, in mid-April, security forces attacked by Boko Haram at the fishing village of Baga turned their guns on civilians after the militants fled. Witnesses told the AP that 187 civilians were killed by security forces who razed the village.

The military said 37 civilians were killed. There has been no investigation and no repercussions for the perpetrators.