The air force loyal to Egypt-backed Libyan strongman Khalifa Haftar said it had joined the Egyptian air strikes on Friday following the attack on Copts that killed 29 people.
But the only confirmed strikes appear to have hit a pro-Al-Qaeda group in the Libyan city of Derna that has fought against IS.
ISIS said on Saturday that its fighters had ambushed the Christians as they were travelling to the Saint Samuel monastery in Egypt’s southern province of Minya.
The shooting was the latest in a series of attacks by IS that have killed more than 100 Copts since December.
Egypt’s Foreign Minister Sameh Shoukry told his US counterpart Rex Tillerson that the jihadists who attacked the Christian convoy had trained in Libyan militant camps.
“There was enough information and evidence of the terrorist elements involved in the (attack) having trained in these camps”, a foreign ministry statement quoted him as saying.
A spokesman for the pro-Al-Qaeda Majlis Mujahedeen Derna, which controls the city in eastern Libya, said the Egyptian air force carried out eight raids on the city without causing casualties.
A Libyan air force statement said: “The operation was a success and the losses of the Al-Qaeda terrorists were heavy in casualties and equipment.”
Majlis Mujahedeen Derna ousted IS from Derna in 2015 and also fights Haftar’s forces.