The Islamic State released a video on Sunday that showed the beheadings of 21 Egyptian Christians in Libya. Hours after the release, Egyptian President Abdel Fattah al-Sisi warned that his country would respond to the deaths.

The five-minute video showing the deaths has been confirmed as authentic. It appeared on the Twitter feed of a pro-Islamic State website.

Militants in black march orange-clad hostages to a beach reportedly near Tripoli. The hostages were forced to kneel. A caption reads: “The people of the cross, followers of the hostile Egyptian church.” One of the militants stands with a knife in his hand before the killings. He states: “Safety for you crusaders is something you can only wish for.”

Thousands of Egyptians have traveled to Libya since the 2011 uprising in Egypt in order ot seek work despite their own government’s advice not to.

The sea was painted red from the blood of the innocent victims whose beheading was captured live.

It is possible that the masked ISIS militant is “jihadi John” who achieved global notoriety after footage showing the death of photojournalist James Foley.

The Egyptians shown in the footage had been captured two months ago.

“The sea you have hidden Sheikh Osama bin Laden’s body in, we swear to Allah we will mix it with your blood,” states the video.