"Those traitors breached all the religious principles and humanitarian values," says Egypt's Grand Mufti Shawqi Allam. Egypt carried out strikes in Libya on militants officials said were involved.
Friday's deadly assault was the latest attack against the Coptic Christian minority. A 70-year-old woman who was stripped and dragged through the streets last year is pursuing justice in court.
Francis noted that schoolchildren were aboard the aircraft thought to have been deliberately crashed by its co-pilot. The pontiff also paid tribute to "martyrs" killed for their faith.
The small hamlet of el-Aour is reeling from the massacre of 13 of its men in Libya, where they worked. A lack of jobs in Egypt means laborers still head to neighboring Libya, despite the danger.
The footage is supposed to show militants from the self-declared Islamic State executing 21 Coptic Christians captured by the extremist group last week.