Egypt carried out air strikes against ISIL group targets in Libya on Monday after the Takfiris posted a video showing the decapitation of 21 Coptic Christians, the military said.

Egypt carried out air strikes against ISIL group targets in Libya on Monday after the Takfiris posted a video showing the decapitation of 21 Coptic Christians, the military said.

"Your armed forces on Monday carried out focused air strikes in Libya against Daesh camps, places of gathering and training, and weapons depots," the military said in a statement, using the Arabic acronym for ISIL.

State television showed footage of Egyptian fighter jets it said were taking off to conduct the strikes.

"The air strikes hit their targets precisely, and the falcons of our air forces returned safely to their bases," the military's statement said.

"We affirm that avenging Egyptian blood and retaliating against criminals and killers is a duty we must carry out."

The air strikes came hours after the Takfiris posted gruesome footage of the beheadings on the Internet, sparking outrage in Egypt and demands for revenge.

A visibly angry President Abdel Fattah al-Sisi said Egypt "reserves the right to respond in a suitable way and time" in a televised speech, and declared seven days of mourning.

Hours after the Egyptian warplanes bombed ISIL targets, foreign ministry said "tough intervention" against militants in Libya is needed or they would threaten world peace.

FM Sameh Shoukry "will head to Washington to take part in an anti-terrorism summit to affirm Egypt's fixed stance on terrorism", his ministry said in a statement.

"Leaving matters as they are in Libya without tough intervention to curb these terrorist organizations represents a clear threat to international security and peace," the statement added.