isis turkey tank
An Islamic State fighter walks near a black flag belonging to the Islamic State as a Turkish army vehicle takes position near the Syrian town of Kobani, as pictured from the Turkish-Syrian border near the southeastern town of Suruc, Sanliurfa province October 7, 2014. Reuters/Umit Bektas

Update as of 3:58 a.m E.T.: At least 40-50 militants have been killed in airstrikes against the Islamic State group in Libya, according to Libya's Air Force Commander Saqer al-Joroushi. "There are casualties among the individuals, ammunition and the communication centers belonging to them. The number of deaths are not less than 40 or 50 for sure," he told Egyptian state television, according to Reuters.

Original story: Egyptian war planes struck ISIS targets in Libya, shortly after President Abdel Fatah al-Sisi said the country had the “right to respond” to the murder of Egyptian Christians, authorities said Monday.

A spokesperson for Egypt's Armed Forces General Command announced the strikes on state radio, the Guardian reported. This is the first time that Egypt has acknowledged taking military action against the Islamic State group.

The statement said the warplanes targeted ammunition and weapons caches and training camps, before returning safely. “Let those far and near know that Egyptians have a shield that protects them,” it said.

Libya's air force reportedly confirmed that it had also launched air strikes against the city of Derna, which fell to an ISIS affiliate last year, The Washington Times reported.

The bombing comes in response to a video reportedly showing the beheading of 21 Coptic Christians in Libya. Libyan army officials have vowed to assist Egypt in any military actions it might take.

Speaking on national television hours after the video was released, Sisi had earlier said that Cairo had the "right to respond in a suitable way and time to punish these murderers," Al Jazeera reported.

Egyptian state news agency MENA confirmed the deaths with the Coptic Church, Reuters reported.

The United States, in a statement, called the killing “despicable and cowardly.”

A Libyan army official had said earlier on Monday that it would support Egyptian intervention. “We strongly support Egyptian military intervention to strike Daaesh [an alternate name for ISIS] and other terrorist groups,” Major General Khalifa Haftar told Egyptian TV channel Dream on Monday, The Tripoli Post reported. "Libyans are helping the Egyptian army to take revenge on these terrorist forces because Cairo is considered to be a Libyan city."

The five-minute video that triggered the retaliation showed the captives being marched onto a beach by masked militants, who then forced them onto their knees and beheaded them. The video’s caption called them: "The people of the cross, followers of the hostile Egyptian church."

Libya’s Coptic Orthodox church has 60,000 followers, or 1 percent of its population, according to the Looklex Encyclopedia. Thousands of Egyptians have traveled to Libya looking for work, after the 2011 uprising that triggered the Arab spring left the country’s economy flagging.

"These people are not in Libya for tourism, for joy, to steal or even to beat others, these people went to Libya to work and earn some money," Shehata Walham, the brother of one of the victims, told the BBC.

The U.S. Copts Association reported on Sunday that 21 more victims have been kidnapped by ISIS affiliates known as Fajr Libya (Libyan Dawn). The victims were reportedly fishermen, kidnapped from the city of Misrata, due about three hours east of the capital of Tripoli.

Libya has been in chaos ever since the 2011 overthrow of former leader Muammar Gaddafi. A number of Islamist groups have been active in the area, including several that have declared ties to ISIS.