A VIDEO has emerged purporting to show the beheading of 21 Egyptian Christians who had been kidnapped by Islamic State (IS) militants in Libya.

In the footage, captives in orange jumpsuits are marched by militants to a beach the group claim is near Tripoli, before being forced to their knees and beheaded.

A caption on the five-minute clip stated: "The people of the cross, followers of the hostile Egyptian church."

The kidnapped Egyptian workers, all Coptic Christians, were seized from the coastal town of Sirte in eastern Libya, now under the control of Islamist groups.

On Friday, IS released pictures of them, saying they had been kidnapped to avenge the fate of Muslim women "tortured and murdered by the Coptic church of Egypt".

Egypt's state news agency MENA quoted the spokesman for the Coptic Church as confirming that the Christians were dead.

The country's National Defence Council will now meet in emergency session to discuss its response to the killings, while President Abdel Fattah al-Sisi has declared seven days of national mourning.