Islamic State in Iraq and the Levant (ISIL) released a video on Sunday that it said showed its fighters beheading 21 Egyptian Christians who were kidnapped in Libya.
The reported killings raise the possibility that the armed group — which controls about a third of Syria and Iraq in a self-declared “caliphate” — has established a direct affiliate less than 500 miles from the southern tip of Italy. One of the fighters shown in the video, speaking English, makes direct reference to that possibility, saying the group now plans to "conquer Rome."
In the video, men wearing black march the captives, dressed in orange jump suits, to a beach. They are forced to their knees, then beheaded. The video appeared on the Twitter feed of a website that supports ISIL.
Al Jazeera could not immediately verify whether the video was authentic, but armed groups in Libya claiming affiliation with ISIL had been holding 21 Egyptian Coptic Christians hostage for weeks.
Egypt's state news agency MENA quoted Coptic Church officials as confirming that 21 Egyptian Christians believed to be held by Islamic State were dead.
A caption on the five-minute video read: "The people of the cross, followers of the hostile Egyptian church."
The group said the killings were revenge for "Muslim women persecuted by Coptic crusaders in Egypt." It did not elaborate on the accusation.
The Egyptian government declared a seven-day mourning period and President Abdel Fattah el-Sisi convened an emergency national security meeting to discuss a response. He sent condolences to "the victims of terrorism," according to a statement released by the presidency.
"These cowardly actions will not undermine our determination," said Sisi, who also banned all travel to Libya by Egyptian citizens in response to the video. "Egypt and the whole world are in a fierce battle with extremist groups carrying extremist ideology and sharing the same goals."
Sisi has repeatedly expressed concerns about armed groups based in Libya who are reportedly seeking to topple his government.
Those fighters have reportedly made contact with Sinai Province, a group operating from Egypt's Sinai Peninsula. Amid ISIL's declaration of an Islamic state, it changed its name from Ansar Beyt al-Maqdis and pledged allegiance to ISIL.
The Coptic Church in a statement called on it followers to have "confidence that their great nation won't rest without retribution for the evil criminals."
Qalini Sanyout, whose two nephews were among the hostages, answered the phone Sunday night amid the sound of wailing in the background.
"What can we say? Can someone tell us if this is true," he told The Associated Press repeatedly. "The whole village is in mourning. Men are covering their heads with dust and mud."
Thousands of Egyptians have traveled to neighboring Libya in search of jobs since an uprising at home in 2011, despite advice from their government not to go to one of the most dangerous countries in the region.
The makers of the video identify themselves as the Tripoli Province of ISIL. Fighters tied to ISIL have perpetrated deadly attacks in the restive North African nation in recent months. In January, gunmen attacked a hotel in Tripoli, killing at least eight people. SITE international security monitoring service said an armed group claiming affiliation with ISIL had claimed responsibility.
Before the killings shown in the video, one of the fighters stood with a knife in his hand and said: "Safety for you crusaders is something you can only wish for."
Al Jazeera and wire services