Abuja, Jun 4 (IANS/EFE): Human rights watchdog Amnesty International on Wednesday denounced the death of 8,000 people at the hands of the Nigerian army during the struggle with Boko Haram in the north of the country, calling the murders war crimes and possible crimes against humanity.

In a report entitled "Stars on their Shoulders, Blood on their Hands: War Crimes Committed by the Nigerian Military," released on Wednesday here, Amnesty collected testimonies and case-files documenting the use of torture, extrajudicial executions and arbitrary detention of thousands of young people and children in the chaos following Boko Haram.

After the attacks of Boko Haram in the northeast stronghold of the terrorists, the army often launched "mop-up", during which most of the killing took place.

"The highest levels of Nigeria's military command, including the chief of army staff and chief of defence staff, were regularly informed of operations conducted in northeast Nigeria," the report claimed.

The most serious case documented by the NGO took place on March 14, 2014 when the army killed more than 640 detainees who had fled the Giwa barracks after a terrorist attack.

An army veteran testified to orders he had received: "Soldiers go to the nearest place and kill all the youths. People killed may be innocent and not armed," he told Amnesty.

According to the report, since 2009 at least 20,000 young people were arrested including children as young as nine years, and in most cases the arrests were arbitrary, since "almost none of those detained have been brought to court".

The conditions in which the detainees were held were also discussed in the report: "Sometimes we drank people's urine, but even the urine you at times could not get," a former detainee told Amnesty.

"Hundreds have been killed in detention either (by soldiers) shooting them or by suffocation," an official told the NGO.

The organisation called for an investigation to hold those responsible accountable, whether soldiers, mid-level or senior officers in the army.

"We call on newly-elected President Buhari to end the culture of impunity that has blighted Nigeria and for the African Union and international community to encourage and support these efforts."