Nigeria's secret police faced questions Monday about how 21 detainees were killed during an attempted jailbreak from their headquarters, with claims of a cover-up about exactly what happened.
The detainees, reportedly suspected Boko Haram insurgents, died Sunday after the Department of State Services said that one inmate overpowered a guard and seized his weapon.
The DSS, which is Nigeria's intelligence agency, has not revealed the charges the suspects faced or exactly how they came to be killed.
But the agency's spokeswoman Marilyn Ogar said in an interview: "All of the 21 were killed by... operatives of the DSS.
"The investigation is still ongoing. We will determine who shot who and at what point and how many were shot by whom and for what reason," she told the Raypower 100.5 FM radio station.
Ogar said the gun seized by the inmate had more than 90 rounds of live ammunition and that he had fired it sporadically.
Gunfire heard for several hours in and around the headquarters were simply warning shots in case the detainees had outside help, she added.
Nigeria's presidency played down the incident but several media outlets questioned the official version of events.
A report on the widely read Premium Times website questioned why so much heavy weaponry was required to subdue one inmate.
Any security breach at DSS headquarters would be an embarrassment for the government but even more so if it involved Boko Haram, which has been waging a violent insurgency in Nigeria's north since 2009.
Nigeria's military has been under pressure about the effectiveness of its strategy to tackle the insurgents in the face of an upsurge in violence that is estimated to have left more than 1,500 dead so far this year.
Amnesty International on Monday claimed that some 600 Boko Haram suspects may have been killed after a jailbreak at a military detention facility in Maiduguri, the state capital of Borno, on March 14.
The human rights monitor quoted witnesses as saying that the military summarily executed hundreds of escapees.
The military had said dozens escaped.