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 kidnapped Egyptian workers, all Coptic Christians, were seized in separate incidents in December and January from the coastal town of Sirte in eastern Libya, under the control of Islamist groups.
The video of the beheadings was posted online by Libyan jihadists who pledge loyalty to IS. It was one of the first such videos to come from an IS group outside its core territory in Syria and Iraq.
The video describes the Copts as "crusaders" and refers among other things to two women, wives of Coptic priests, whose alleged conversion to Islam triggered a sectarian dispute in Egypt in 2010.
IS militants claim to have carried out several attacks in Libya, which in effect has rival governments. (+ BBC video) » | Monday, February 16, 2015