The Cairo-based top Muslim body Al-Azhar on Monday condemned the executions of some 30 Ethiopian Christians captured in Libya by the Islamic State group.
The Islamic State released a 29-minute video on Sunday purportedly showing the executions, with one group of men being beheaded by masked militants on a beach and another group being shot in the head in a desert area.
Al-Azhar, Sunni Islam's prestigious seat of learning, condemned the "heinous terrorist crime committed by terrorist group Daesh," it said on its Facebook page, using the Arabic acronym for Islamic State.
The actions of "Daesh and other similar organisations do not comply by any means with any religion, human laws and customs," it said.
Egyptian President Abdel Fattah al-Sisi's office also denounced the killings, and called for an international effort to end the crisis in Libya.
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The international community must "assume its responsibility and support Libya's national army, the Libyan government, and the elected parliament through swift and effective steps to settle the crisis in Libya," it said in a statement.
It said efforts must be taken to "restore the Libyan state and its security and stability, as well as halting money and arms flows to terrorist and extremist groups present in Libya".
In February, Cairo carried out air strikes against Islamic State group targets inside Libya after the jihadists beheaded 20 Egyptian Coptic Christians.
The Copts had travelled to Libya for work when they were kidnapped and executed by Islamic State militants.
Since their beheadings, Sisi has insisted in forming a joint Arab military force to fight extremist groups in the region.
On Wednesday, Arab military chiefs will meet in Cairo to discuss forming such a force after Arab League leaders agreed to create it at a March summit in Egypt.