Men in orange jumpsuits purported to be Egyptian Christians held captive by the ISIS are marched by armed men along a beach said to be near Tripoli, in this still image from an undated video made available on social media on February 15, 2015.

Egypt’s Coptic Orthodox church said Sunday it was “confident” that those who purportedly beheaded a group of Egyptian Copts in Libya will be punished.

“The Orthodox church … is confident its homeland would not rest until the evil perpetrators get their fair retribution for their wicked crime,” the Coptic church said in a statement on its Facebook page.

On Sunday, militants from the Islamic State of Iraq and Syria (ISIS) released a video purportedly showing the beheading of Egyptian Copts captured in Libya.

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

In a separate development, the United States condemned as “despicable” the beheading of the 21 men.

“The United States condemns the despicable and cowardly murder of twenty-one Egyptian citizens in Libya by ISIS-affiliated terrorists,” White House spokesman Josh Earnest said.

“ISIS’s barbarity knows no bounds. It is unconstrained by faith, sect, or ethnicity,” Earnest added, saying the latest bloodshed “only further galvanizes the international community to unite against ISIS”.

“This heinous act once again underscores the urgent need for a political resolution to the conflict in Libya,” Earnest said.

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 distributed by militants on social media.

Family members of 27 Egyptian Coptic Christian workers kidnapped in the Libyan city of Sirte, take part in a sit-in inside the compound of Saint Mark’s Coptic Orthodox Cathedral to call for the release of their relatives, in Cairo.

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