Gunmen killed at least 235 people and injured scores at a packed mosque in Egypt's restive North Sinai province on Friday, in one of the country's deadliest attacks in recent memory.
A bomb explosion ripped through the Rawda mosque roughly 40 kilometres west of the North Sinai capital of Arish before gunmen opened fire on the worshippers gathered for Friday prayers, officials said.
The Egyptian government has declared three days of mourning after the attack.
The victims included civilians and conscripts praying at the mosque.
Officials said the attackers were travelling in four off-road vehicles.
President Abdel Fattah El Sisi convened an emergency security meeting soon after the attack, state television reported, and three days of national mourning were declared.
There was no immediate claim of responsibility for the attack but ISIL's Egypt branch has killed hundreds of policemen and soldiers in the north of the Sinai peninsula, as well as civilians accused of working with the authorities.
They have also targeted followers of the mystical Sufi branch of Sunni Islam and Christians.
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A tribal leader and head of a Bedouin militia that fights ISIL told Agence France-Presse that the mosque was known as a place of gathering for Sufis.
ISIL shares the puritan Salafi view of Sufis as heretics for seeking the intercession of saints.
The militants had previously kidnapped and beheaded an elderly Sufi leader, accusing him of practising magic, and abducted Sufi practitioners later released after "repenting".
The group has killed more than 100 Christians in church bombings and shootings in Sinai and other parts of Egypt, forcing many to flee the peninsula.
The military has struggled to quell the militants, who pledged allegiance to ISIL in November 2014.
ISIL regularly conducts attacks against soldiers and policemen in the peninsula bordering Israel and the Palestinian Gaza Strip, although the frequency and scale of such attacks has diminished over the past year.
They have since increasingly turned to civilian targets, attacking not only Christians and Sufis but also Bedouin Sinai inhabitants accused of working with the army.
Aside from ISIL, Egypt also faces a threat from Al Qaeda-aligned militants who operate out of neighbouring Libya.
A new group calling itself Ansar Al Islam claimed an October ambush in Egypt's Western Desert that killed at least 16 policemen.
Many of those killed belonged to the interior ministry's secretive National Security Service.