Egypt responded quickly to the release of video documenting the beheading of 21 men.
Egypt says it has bombed Islamic State targets in Libya, hours after the militants released video of apparent beheadings of 21 Egyptian Christians.
State TV said the dawn strikes had targeted camps, training sites and weapons storage areas. A second wave of strikes was reported hours later.
Libyan officials said Egypt hit targets in the militant-held city of Derna.
The strikes came amid widespread condemnation of the killings. The US and UN described them as "cowardly".
A video emerged on Sunday showing militants forcing a group of men to the ground and decapitating them.
The strikes came in two waves after Egypt's President Abdel Fattah el-Sissi went on national television in the world's most populous Arab nation and vowed revenge was coming. The address was followed by the airing of military video showing the planes taking off for the mission and an Armed Forces General Command statement saying the strikes were "to avenge the bloodshed and to seek retribution from the killers."
"Avenging Egyptian blood and punishing criminals and murderers is our right and duty," the Egyptian military said in the statement, which was broadcast on state television.
Concern has increased over ISIS' rising influence in Libya amid the power and security vacuum prevalent in the country since the 2011 uprising that overthrew former dictator Moammar Gadhafi.
CNN reported in November that fighters loyal to ISIS had complete control of the city of Derna, which has a population of about 100,000 and is situated not far from the Egyptian border.
Jihadists with allegiance to ISIS had also expanded their presence westward along the Libyan coast, forming chapters in cities including Benghazi, Sirte and even Tripoli, the capital, according to Noman Benotman, a former Libyan jihadist now involved in counterterrorism for the Quilliam Foundation.
LONDON — Italy warned that ISIS is at Europe's doorstep as France and Egypt called for the United Nations Security Council to meet over the spiraling crisis in Libya.
The growing alarm came as Egyptian jets bombed ISIS targets in the North African nation as revenge for the beheadings — documented in an ISIS propaganda video — of 21 Coptic Christian Egyptian nationals in Libya.
The release of the video has underscored fears that ISIS is taking advantage of the chaos in Libya to expand its reach and stake a firmer foothold there.
French President Francois Hollande spoke by phone with his Egyptian counterpart, President Abdel-Fattah el-Sissi, to discuss the situation in Libya on Monday, according to Hollande's office. It said the two spoke of the growth of ISIS in Libya and "underscored the importance of the security council meeting and for the international community to take new measures" against the threat.
Libya has been unraveling since the overthrow of Moammar Gadhafi in 2011. There are rival governments operating under separate parliaments — each with their own security brigades — and a plethora of armed Islamist groups jockeying for control.