Egypt right groups condemn execution of 15 prisoners
In a late Tuesday statement, the groups said legal procedures against them were flawed and at least one of the 15 appears to have been tortured in detention.
They also said relatives were not allowed to see them on the day of their execution, as the law requires.
Tuesday’s hangings in two prisons near Cairo were the largest known number of executions on a single day since the insurgency in northern Sinai escalated four years ago.
The hangings come a week after the Islamic State group attacked a helicopter with an anti-tank missile at a North Sinai airport as the country's defence and interior ministers were visiting.
The ministers were unhurt in the attack but an aide to the defence minister was killed along with a pilot.
Egypt's IS affiliate has killed hundreds of policemen and soldiers in attacks in the Sinai and also targeted civilians in the mainland.
Egyptian courts have sentenced hundreds to death over unrest since the military ousted elected president Mohamed Morsi in 2013.
Six militants were executed in 2015 following their conviction by a military tribunal on terror charges.