On Sunday, ISIS released a video that claims to show the beheading of a group of Egyptian Christians who had been kidnapped in Libya several weeks ago. A spokesman for the Coptic Church has said via Egypt’s state news agency MENA that the 21 captives are dead.

The five-minute video shows the captives, dressed in orange jumpsuits, being marched to a beach, each accompanied by a masked, knife-wielding militant in black. The video indicates that the location is near Tripoli. The hostages are forced to their knees, then beheaded. The video is titled “A Message signed with blood to the nation of the cross.”

Prior to the killings one of the militants, who is dressed differently than the others, addresses the camera, saying “Safety for you crusaders is something you can only wish for.” After the execution, the speaker points northward and says “We will conquer Rome, by Allah’s permission.”

Twenty-one Egyptian Coptic Christians had been held hostage in Libya for weeks, kidnapped in two separate incidents in the Libyan city of Sirte. The video makers identify themselves as the Tripoli Province of ISIS. The captured men had been identified by relatives in media released by ISIS, including an online magazine that was published a few days ago.

Mina Thabet, who is a researcher at the Egyptian Commission for Rights and Freedoms, faulted the country’s government for what he called a delayed response to the hostage crisis. His organization has had regular communication with the hostages’ families. Thabet said that he believed that all of the victims in the video were Egyptian except one, who was most likely from sub-Saharan Africa.

The release of the video occurred on the day after ISIS took control of Sirte, now the third town in Libya held by the militants. Tens of thousands of Egyptians work and live in Libya. Egypt made an announcement on Friday that they will facilitate the exit of the Egyptians living in the country.

Global security firm Flashpoint Intelligence said that the beheading of the Egyptian Christians means that ISIS now views Christian populations as targets, as well as part of the “Crusader plot.” A Flashpoint report said that the group’s message is “highly intimidating,” and challenges Western nations to intervene to save Christians.

Egyptian President Abdel Fattah el Sisi has declared seven days of national mourning.