Pope Francis offered Mass Tuesday in honor of the 21 Egyptian Coptic Christians who were ruthlessly beheaded by Islamic State militants in Libya, while also condemning man’s capability for evil and destruction.

At the Vatican’s Santa Marta Chapel, the Pope asked the congregation to join him in prayer for “our brother Copts, whose throats were slit for the sole reason of being Christian, that the Lord welcome them as martyrs…”

During his homily, Pope Francis warned about “merchants of death,” whom he described as business people who sell weapons to those at war and perpetuate a cycle of hate and violence, the Vatican said.

The Mass was attended by the Pope’s personal secretary, Abuna Yoannis Lahzi Gaid, who is a Coptic Catholic.

A day earlier, Pope Francis denounced the beheadings, calling it a "barbaric assassination.”

Francis also phoned the patriarch of the Coptic Orthodox Church, Pope Tawadros II, to "express his profound participation with the pain of the Coptic Church for the recent barbaric assassination of Coptic Christians by Islamic fundamentalists," the Vatican spokesman said.

Francis referred to the killings Monday during an audience with a Scottish ecumenical delegation. "They only said 'Jesus help me ...' The blood of our Christian brothers is testimony that cries out. Be they Catholic, Orthodox, Copts, Lutherans, it doesn't matter: They're Christian!"

Militants in Libya affiliated with the Islamic State group released a video late Sunday purporting to show the mass beheading of Coptic Christian hostages held for several weeks.

The killings raised anxieties in Italy, given Libya's proximity just across the Mediterranean Sea and because one of the militants in the video said the group plans to "conquer Rome," the seat of Catholicism.

The Associated Press contributed to this report.