According to Saleh, the attackers had done this in a bid to erase their fingerprints so that they could not be identified.
He said they committed suicide in the end, using handgrenades.
Saleh also said efforts were being made using advanced technology with the help of foreign allies to identify the bodies, but stressed he could not disclose further progress due to the sensitivity of the investigation at this stage.
He also did not say how many attackers killed themselves.
Daesh (IS-K) claimed responsibility for the attack last Monday which resulted in the death of at least 30 civilians, mostly students.
Meanwhile, Saleh said that Yama Siawash, a former journalist and employee of the Central Bank, died in an explosion Saturday from an IED that was made with military grade RDX explosive material.
He said this was not “home made” explosive compounds.
Two kilograms was used in the explosive device which had been attached to his vehicle close to the fuel tank.
Siawash died along with two of his colleagues in Kabul city.
No group has claimed responsibility for the attack.