Nigeria's army said on Wednesday it had released 128 detainees held on suspicion of being Boko Haram militants, two months after nearly 200 others were freed after security screening.
Human rights groups have repeatedly accused the military of arbitrary detention of civilians in the country's northeast, which has been wracked by Islamist violence in the last six years.
Senior commanders have strongly rejected claims of wrongful imprisonment, torture, ill-treatment and even extra-judicial killings of prisoners.
A batch of 182 detainees was released in early July and on Wednesday 128 more -- 109 men, seven women and 12 boys -- were handed over to the Borno state governor Kashim Shettima in Maiduguri.
All had been arrested across the state as part of counter-insurgency operations, said Nigeria's highest-ranking army officer, Lieutenant General Tukur Buratai, who was at the ceremony.
They were declared "clean" after screening from military intelligence officers, the police and members of the Department of State Security or secret police, the chief of army staff added.
"This is (a) clear manifestation that the army is clearly professional," Tukur said at the handover.
Amnesty International said in June there was sufficient evidence for the International Criminal Court to probe senior Nigerian officers for war crimes because of the treatment of detainees.
At least 20,000 mostly young men and boys have been arrested during the conflict while hundreds of people were unlawfully killed and thousands more died in military custody, the group alleged.
UN rights chief Zeid Ra'ad Al Hussein echoed Amnesty's concerns.
President Muhammadu Buhari, who has made defeating Boko Haram a priority and vowed to review military rules of engagement to try to end concerns about rights violations, has promised to probe the claims.
Last month he gave his new team of military three months to defeat the Islamic State group-allied rebels, whose insurgency has left at least 15,000 dead and displaced more than two million since 2009.