Egyptian warplanes struck Islamic State targets in Libya on Monday in swift retribution for the extremists' beheading of a group of Egyptian Christian hostages on a beach, shown in a grisly online video released hours earlier.
Egyptian, Libyan Airstrikes Target IS in Libya

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Egyptian Coptic men mourn for 21 Coptic Egyptian men slain by Islamic State militants in Sirte, Libya, at the Virgin Mary Church in the village of el-Aour, near Minya, 220 kilometers (135 miles) south of Cairo, Egypt, Feb. 16, 2015.

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A woman mourns over Egyptian Coptic Christians who were beheaded by the Islamic State group at the Virgin Mary Church in the village of el-Aour, near Minya, 220 kilometers (135 miles) south of Cairo, Egypt, Feb. 16, 2015.

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An Egyptian man holds a poster with Arabic that reads "Muslims and Copts are in the same tragedy" during a protest against the slaying of Egyptian Coptic Christians in Libya by militants associated with the Islamic State group, in Cairo, Egypt, Feb. 16, 2

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Neighbors and friends of relatives of the Egyptian Coptic men killed in Libya sit at the courtyard of the Virgin Mary Church in the village of el-Aour, near Minya, 220 kilometers (135 miles) south of Cairo, Egypt, Feb. 16, 2015.