The Islamic State (ISIL) group in Libya has released a video purportedly showing the beheading of 21 Egyptian Coptic Christians, prompting Egypt’s president to threaten a “suitable” punishment for the killings.

President Abdel Fattah al-Sisi said his country reserved the right to “punish these murderers” as he called a meeting of security chiefs and declared seven days of mourning after the video was released by jihadists on social media.

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The footage released by ISIL online shows 21 handcuffed hostages wearing orange jumpsuits being beheaded by their black-suited captors in a coastal area the group said was in the Libyan province of Tripoli.

In the latest issue of the ISIL online magazine Dabiq, the group said the same number of Egyptian hostages were being held in Libya.

According to the New York Times, this is the first time Islamic State militants have shown a killing outside of the territory it controls in Syria and Iraq.

Screenshot video showing Egyptian ISIL victims being marched to their beheadings. Photo: Screenshot

The Coptic Church issued a statement saying it was “confident” the killers would be brought to justice as it confirmed those beheaded were Egyptian Copts, while Al-Azhar, the prestigious Cairo-based seat of Islamic learning, denounced the “barbaric” killings.

Egyptian state television broadcast some of the footage from the ISIL video without showing the beheadings but showed the hostages marched along by their captors on a beach.

“Egypt reserves the right to respond in a suitable way and time to punish these murderers,” a visibly angry Sisi said in a televised speech.

The security body that is meeting in Cairo includes Sisi, his defence and interior ministers and military commanders.

Egypt last year denied reports of having carried out air strikes on Islamists in Libya, but US officials said its ally the United Arab Emirates carried out the strikes using Egyptian bases.

French President Francois Hollande, whose government has agreed to sell Egypt advanced Rafale fighter jets, expressed his “concern at the expansion of Daesh in Libya,” referring to the Islamic State group.

The group has been hammered by a US-led air strikes in Iraq and Syria after it took over swathes of the two countries, and has active affiliates in Egypt and Libya.

Sunday’s video, entitled “A message signed with blood to the nation of the cross”, has a scrolling caption in the first few seconds referring to the hostages as “People of the cross, followers of the hostile Egyptian Church”.

One of the masked captors, wearing a military uniform and pointing a knife to the camera said in English: “Today we are in the south of Rome, in the land of Islam Libya … the sea you have hidden Sheikh Osama bin Laden’s body in, we swear to Allah we will mix it with your blood.”

Al-Qaeda founder Bin Laden was shot and killed in a dramatic helicopter raid by US special forces in Pakistan in the early hours of May 2, 2011 and later buried at sea in an unidentified location.

AFP