CAIRO (Reuters/AFP) - Egypt's military said in a statement on state television that it had carried out an air strike against Islamic State in Iraq and Syria (ISIS) targets in Libya at dawn on Monday, a day after the group released a video appearing to show the beheading of 21 Egyptians there.

The attack focused on ISIS camps, training sites and weapons storage areas across Egypt's border in Libya, where Islamist militants have thrived amid chaos.

"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 ISIS.

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 militants posted gruesome footage of the beheadings on the Internet, sparking outrage in Egypt and demands for revenge.

ISIS in Libya released a video purportedly showing the beheading of 21 Egyptian Coptic Christians, prompting Egypt's president to threaten a "suitable" punishment for the killings.

President Abdel Fattah al-Sisi said his country reserved the right to "punish these murderers" as he called a meeting of security chiefs and declared seven days of mourning after the video was distributed by jihadists on social media.

The footage shows 21 handcuffed hostages wearing orange jumpsuits being beheaded by their black-suited captors on a beach the group said was in the Libyan province of Tripoli.