Updated

Seven Egyptian rights groups have condemned the execution of 15 suspected Islamic militants convicted of staging a deadly attack on an army checkpoint four years ago in the Sinai Peninsula.

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.

Six militants were executed in 2015 following their conviction by a military tribunal on terror charges.