WASHINGTON, Feb. 15 -- The White House on Sunday described murders of 21 Egyptian citizens in Libya by the Islamic State as "despicable and cowardly" and urged the Libyans to reject extremist groups and all acts of terrorism.

"This wanton killing of innocents is just the most recent of the many vicious acts perpetrated by ISIL-affiliated terrorists against the people of the region," said a White House statement, adding that the incident only further galvanized the international community to unite against IS.

The statement also called for a political resolution to the conflict in Libya, warning that continued internal conflicts only benefit terrorist groups.

On Sunday, the IS militant group published a video purportedly showing the beheading of 21 Egyptian Coptic Christians abducted in Libya. Later, the Egyptian Orthodox Church confirmed the killing.

Egyptian President Abdel Fattah al-Sisi said that his country reserves the right to respond at a proper time to the mass killings.