A Human Rights Watch report said refugees were being coerced, threatened and forced to leave Pakistan and return to war-torn Afghanistan
Save the Children said Taliban's growing influence and Pakistan's repatriation policy are key reasons for the looming crisis
No group immediately claimed responsibility for the attack, but militants such as Taliban and the Islamic State group have previously carried out similar attacks
The attack comes as the US administration contemplates whether to send more troops to rein in attacks in the war-strife country
Afghan soldiers were killed by Taliban attackers disguised in military uniforms in what would be the deadliest attack ever on an Afghan base
US-Forces Afghanistan had said earlier that if confirmed, the death of the Hasib and his associates would "significantly degrade ISIS-K operations in Afghanistan and help reach our goal of destroying them in 2017."