VATICAN CITY - Pope Francis denounced the slaying of Egyptian Copts in Libya by Islamic State of Iraq and Syria (ISIS)-affiliated militants on Monday, calling it a "barbaric assassination" of innocents who were killed merely for being Christian.

Francis 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 also 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!"

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Militants in Libya affiliated with ISIS 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.

Egypt has launched airstrikes against ISIS targets in Libya as a response on Monday.

A spokesman for the Armed Forces General Command announced the strikes on state radio Monday, marking the first time Cairo has publicly acknowledged taking military action in neighboring Libya, where extremist groups seen as a threat to both countries have taken root in recent years.