By LAURA KING

Tribune News Service

CAIRO -- Egypt bombarded Islamic State targets in Libya today and urged coalition allies to do the same, hours after a gruesome video released online by the militant group purported to show the beheadings of 21 Egyptian Christians on a Mediterranean beach.

Training camps and weapons caches were among the targets, and all the aircraft returned safely to base, state television reported. President Abdel Fattah Sisi, the former military chief, had declared earlier that Egypt had the "right to respond" to the murder of its citizens.

Egypt swiftly called on the U.S.-led coalition confronting the Sunni Muslim militant group in Syria and Iraq to expand military actions to target its Libyan branch as well. In a statement, the Foreign Ministry urged strikes against "the terrorist Daesh organization," referring to the group by its Arabic acronym.

The killings of the 21 Coptic Christians sent a wave of revulsion across Egypt, despite the Copts' often disenfranchised status in an overwhelmingly Muslim country. Official statements cast the executions as an attack on all Egyptians, which would be dealt with as such. As a gesture of solidarity, Sisi visited a Coptic cathedral to offer condolences.

"Let those far and near know that Egyptians have a shield that will protect them all and a sword that amputates terrorism and extremism," the Egyptian military command said in a statement, describing the airstrikes as "retribution." Muslim clerics also were quick to condemn the killings, with Egypt's Al Azhar, the seat of Sunni learning, describing the executions as "barbaric."

Later, a senior Libyan air force officer told Egyptian television the Egyptian strikes killed 40 to 50 militants, but the number could not be independently verified.

The executions, condemned by the Obama administration, appeared to signal a determination on the part of the Islamic State to expand its footprint beyond Iraq and Syria, the two countries where it has made its greatest military gains. Libya, which has collapsed into warring factions presided over by rival militias, offers fertile territory for the Sunni Muslim militant group, with enormous oil wealth at stake.

In the grim video, shot on a wintry beach, the prisoners were seen being marched into place by a line of black-clad, knife-wielding captors. At first, they kneel, the lips of some of the doomed men moving in apparent prayer. Then they were forced to lie face-down in the sand, and the executioners reached down and begin sawing away at their necks.

A narration of sorts was delivered by a man wearing camouflage and a light-brown mask, who is seen taking part in the killings -- reminiscent of a figure known in the West as "Jihadi John," who has carried out similar executions in Syria after delivering declarations in British-accented English. In the latest video, the apparent ringleader, speaking colloquial and nearly unaccented English, intones: "This filthy blood is just some of what awaits you."

And in an explicit bid to stress the growing reach of the group and its proximity to European shores, the mass execution is described as taking place on Libya's Mediterranean coast -- "south of Rome."

Unlike some previous Islamic State videos that have cut away before the victims' heads are sawed off, this one presented the beheadings in graphic, jagged jump-cuts, culminating with the severed heads being placed on the backs of the corpses.

Despite growing dangers during the last year as Libya has fallen into deepening chaos, impoverished Egyptian laborers have continued to flock to the neighboring, energy-rich state, where wages are far higher than at home. Many are Christians, and when the two groups of Copts were seized, statements from their Islamist captures made it clear they were targeted primarily for their religion.

Although the government had made overtures to the Coptic Christian community, thought to make up between 10 percent and 15 percent of Egypt's population of approximately 90 million, many Copts consider themselves a downtrodden minority. They face discrimination in jobs and housing, and were singled out for retribution when Islamist President Mohamed Morsi was toppled in a popularly supported coup in 2013.

On Friday, relatives of the kidnapped men, mostly from poor areas in southern Egypt, had staged rallies and prayers in an attempt to galvanize a stronger response from the Egyptian government. Officials assured them all possible steps were being taken to save their loved ones.

On Sunday, Sisi convened an emergency meeting of top security officials, and Egypt's government declared seven days of official mourning.

The Egyptian Christians had been seized in the central Libyan city of Sirte, where fierce fighting had broken out. Libya has been riven for months by armed militias, but with the relatively recent addition of a deadly and dreaded element: fighters declaring their loyalty to the fanatics of the Islamic State, who have gloried in barbaric and well-documented acts in the wide bands of territory they control in Syria and Libya.

Most recently, those have included the death of a young American woman from Arizona, Kayla Mueller, who had been held hostage by the group. Prior to that, the group caused worldwide revulsion when it burned a captured Jordanian pilot to death in a cage.

Victims in recent months have also included a string of Americans and Britons, including journalists and aid workers who were beheaded, and more recently two Japanese nationals beheaded a week apart.