EGYPTIAN warplanes hammered Islamic State (Isis) targets in Libya today, in a furious reaction to a grisly video of the beheading of 21 hostage Egyptian Coptic Christians.

The video which sparked the attacks was released late on Sunday by Libyan fighters affiliated with Isis.

They had been holding 21 Egyptian Coptic Christian labourers rounded up in the city of Sirte in December and January.

An Egyptian armed forces spokesman announced the strikes on state radio, marking the first time that Cairo has publicly acknowledged taking military action in neighbouring Libya — although it is believed to be giving behind-the-scenes support to general Khalifa Haftar, who supports the Tobruk government.

The army said it had targeted weapons caches and training camps, adding that the “intense strikes” were “to avenge the bloodshed and to seek retribution from the killers.”

Libya’s airforce also participated in an attack on the eastern coastal city of Derna.

“There are casualties among individuals, ammunition and Islamic State communication centres,” said Libyan air force Commander Saqer al-Joroushi, adding that between 40 to 50 Isis fighters were killed.

“More air strikes will be carried out today and tomorrow in co-ordination with Egypt,” said Cdr Joroushi, who is loyal to the government which set up in the eastern city of Tobruk after losing control of Tripoli.

It has been confined to the country’s far east since Islamist militias seized Tripoli last year and Islamist politicians reconstituted a previous parliament there.

The Tripoli-based parliament condemned today’s strike as an assault on the country’s sovereignty.

The Egyptian government declared a seven-day mourning period after the release of the video and President Abdel Fattah el-Sissi addressed the nation late on Sunday night.

“These cowardly actions will not undermine our determination” said Mr Sissi, who also banned all travel to Libya by Egyptian citizens.

“Egypt and the whole world are in a fierce battle with extremist groups carrying extremist ideology and sharing the same goals.”