Egyptian security forces face a jihadist insurgency that has killed hundreds of soldiers and policemen
Ansar Bayt al-Maqdis, Egypt's most active militant group, has sworn allegiance to ISIL, a statement from Ansar said Monday night.
Ansar had previously told Reuters that it sought inspiration and advice from ISIL, the radical Al Qaeda offshoot that has taken over swathes of Iraq and Syria, drawing US-led airstrikes as it tries to remake the map of the Middle East.
"After entrusting God we decided to swear allegiance to the emir of the faithful Abu Bakr al-Baghdadi, caliph of the Muslims in Syria and Iraq and in other countries," the statement said.
Egyptian security forces face a jihadist insurgency that has killed hundreds of soldiers and policemen since the army toppled President Mohamed Mursi of the Muslim Brotherhood last year after mass protests against his rule.
Last week the government declared a three-month state of emergency in parts of North Sinai following attacks that killed at least 33 security personnel in some of the worst anti-state violence since Mursi's ouster.
No group has claimed responsibility for the attacks, but similar previous operations have been claimed by Ansar.