A video released on Sunday by the jihadist Islamic State group (IS) on YouTube shows the beheading of more than a dozen men – purportedly Egyptian Christians – on a beach they said was in Libya's Tripoli.
Egypt's presidency confirmed the death of Egyptian hostages and announced a week of mourning, offering condolences to all Egyptians. The National Defence Council has also convened to discuss the situation, while President Abdel-Fattah El-Sisi said Egypt reserves its right to retaliate at the suitable time and place.
Twenty-one Coptic workers, mostly from impoverished villages in Upper Egypt, were kidnapped between late December and early January in the Libyan city of Sirte. Some of the hostages appear in the video.
The five-minute video, produced by IS' media organ Alhayat Media Center, shows in a Hollywood style a group of masked men dressed in black from head to toe. They lead another group of men whose hands are tied behind their backs and wearing orange jumpsuits.
After keeping them on their knees for a while, the men in black lay the victims face down and slit their throats using daggers. After the decapitation they place the heads on the bodies.
A masked militant donning military camouflage uniform – the only IS member not wearing the black uniform in the video – speaks fluent English, albeit with a foreign accent, before and after the execution.
"Oh people, recently you've seen us on the hills of Al-Sham [Greater Syria] and on Dabeq's Plain, chopping off the heads that had been carrying the cross delusion for a long time, filled with spite against Islam and Muslims, and today we… are sending another message: oh crusaders, safety for you will be only wishes."
"Especially when you're fighting us all together, therefore we will fight you all together until the war lays down its burdens and Jesus peace be upon him will descend, breaking the cross, killing the swine," the speaker continues.
He concludes with a reference to Osama Bin Laden, the Al-Qaeda leader who was killed by US forces in 2011. "The sea you've hidden Sheikh Osama Bin Laden's body in, we swear to Allah we will mix it with your blood."
The extremely graphic video, titled A Message Signed with Blood to the Nation of the Cross, ends with a shot of sea water mixed with blood, with jihadist hymns played.
Also near the end a subtitle reads in both Arabic and English, "This filthy blood is just some of what awaits you, in revenge for Camelia and her sisters."
Camelia Shehata was a wife of a Coptic priest who was allegedly detained by the Church after she was said to have converted to Islam. She later denied the claim.
Photos of the hostages and militants, seemingly taken on the same day of the execution, were earlier published by Dabeq, IS' online English magazine that announced the kidnapping of the 21 Copts.
Dabeq had said the kidnapping was to avenge the fate of Muslim women "tortured and murdered by the Coptic church of Egypt" and that the group's expansion into Libya allows it "to easily capture Coptic crusaders."
While pointing towards the sea with his dagger, the masked speaker vowed to "conquer Rome."
The latest high profile case of execution by the Islamic State group took place in early February when the jihadists killed Jordanian pilot Moaz All-Kasasseba – captured after his plane crashed in Syria in December – by burning him alive.
Several Coptic Christians have been killed in Libya in recent years. Last year, the bodies of seven Christians who had been shot were found near the city of Benghazi.