Egyptian fighter jets carried out strikes on Friday directed at camps in Libya which Cairo says have been training militants who killed dozens of Christians earlier in the day, Reuters reported.
President Abdel Fattah al-Sisi said he had ordered strikes against what he called terrorist camps, declaring in a televised address that states that sponsored terrorism would be punished.
Egyptian military sources said six strikes took place near Derna in eastern Libya at around sundown, hours after masked gunmen attacked a group of Coptic Christians traveling to a monastery in southern Egypt, killing 29 and wounding 24.
The Egyptian military said the operation was ongoing and had been undertaken once it had been ascertained that the camps had produced the gunmen behind the attack on the Coptic Christians in Minya, southern Egypt, on Friday morning.
"The terrorist incident that took place today will not pass unnoticed," Sisi said. "We are currently targeting the camps where the terrorists are trained."
He said Egypt would not hesitate to carry out further strikes against camps that trained people to carry out operations against Egypt, whether those camps were inside or outside the country.
Egyptian military footage of pilots being briefed and war planes taking off was shown on state television.
East Libyan forces said they participated in the air strikes, which had targeted forces linked to al-Qaeda at a number of sites, and would be followed by a ground operation.
A resident in Derna heard four powerful explosions, and told Reuters that the strikes had targeted camps used by fighters belonging to the Majlis al-Shura militant group.
Majlis al-Shura spokesman Mohamed al-Mansouri said in a video posted online that the Egyptian air strikes did not hit any of the group's camps, but instead hit civilian areas.
There was no immediate claim of responsibility for the attack on the Christians, which followed a series of church bombings claimed by Islamic State in a campaign of violence against the Copts.
Islamic State supporters reposted videos from earlier this year urging violence against the Copts in Egypt.
At a nearby village, thousands later attended a funeral service that turned into an angry protest against the authorities' failure to protect Christians.