According to Reuters, ISIS released another grisly beheading video on Sunday, this one purportedly showing the execution of 21 Coptic Christians kidnapped in Libya.

Libyan parliament confirmed the deaths yesterday, when photos of the execution were published by an ISIS-affiliated magazine.

The Guardian reports the Egyptian guest workers were abducted from the Libyan city of Sirte during two raids in December and January, apparently "in revenge for" two women allegedly imprisoned by Coptics for converting to Islam.

Earlier this week, Egyptian Prime Minister Ibrahim Mehleb told the hostages' families that the government would "spare no efforts to protect its sons and defend their rights," Daily News Egypt reports.

UPDATE - 4:00 p.m.: According to CBS News' Alex Ortiz, Egyptian President Abdel Fattah el-Sissi has announced seven days of national mourning in response to the video.

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