Amnesty International said Wednesday there was sufficient evidence for the International Criminal Court to probe senior Nigerian military officers for war crimes in the battle against Boko Haram.
The group stated the case against five senior officers in a new 133-page report based on hundreds of interviews, including with military sources and leaked defence ministry documents.
The allegations centre on thousands of people Amnesty claimed were extra-judically murdered by the security forces and its civilian vigilante allies, as well as crimes against those held in military custody.
"In the course of security operations against Boko Haram in north-east Nigeria, Nigerian military forces have extrajudicially executed more than 1,200 people; they have arbitrarily arrested at least 20,000 people, mostly young men and boys," the report said.
Nigerian forces "have committed countless acts of torture; hundreds, if not thousands, of Nigerians have become victims of enforced disappearance; and at least 7,000 people have died in military detention as a result of starvation, extreme overcrowding and denial of medical assistance," it added.
Amnesty said commanders based in the northeast "should be investigated for potential responsibility for war crimes of murder, enforced disappearances and torture".
Top service chiefs in the capital Abuja "should be investigated for their potential command responsibility for crimes committed by their subordinates given that they knew or should have known about the commission of the crimes, and failed to take adequate action".
The ICC in The Hague has opened a preliminary investigation into the Boko Haram conflict, which Amnesty said has killed at least 17,000 people since 2009.
The tribunal has previously said there was insufficient evidence tying Nigeria's military to systematic and orchestrated atrocities targeting civilians.
But the report said: "Amnesty International believes that the evidence contained in this report and submitted separately to the (ICC) Office of the Prosecutor is sufficient to reopen this issue."
The group said it had separately shared its evidence with the ICC prosecutor's office.
Amnesty's latest report includes new claims on specific acts of murder committed by Nigerian soldiers in the northeast but the general subject matter is not new.
Amnesty, Human Rights Watch and independent reporting, including by AFP, has found evidence of arbitrary killing, unlawful detention and torture in custody of alleged Boko Haram suspects.
The government of former president Goodluck Jonathan was repeatedly pressured to try all Boko Haram suspects in court.
New President Muhammadu Buhari said after taking the oath of office on Friday that he would review the military's rules of engagement in a bid to end concerns of rights violations by soldiers.
He also promised to improve "operational and legal mechanisms so that disciplinary steps are taken against proven human right violations by the Armed Forces".