The attack targeted a mosque frequented by Sufis, members of Islam’s mystical movement, in the north Sinai town of Bir al-Abd. Islamic militants, including the local affiliate of Daesh, consider Sufis heretics because of their less literal interpretations of the faith.

The Daesh affiliate has been waging a stepped-up campaign of violence in northern Sinai for years and has claimed deadly bombings on churches in the capital, Cairo, and other cities, killing dozens of Christians. It also is believed to have been behind the 2016 downing of a Russian passenger jet that killed 226.

This was the first major militant attack on a Muslim mosque and the startling bloodshed eclipsed any past attacks of its kind, even dating back to a previous Islamic militant insurgency in the 1990s.

The militants opened fire from four off-road vehicles on worshippers inside the mosque during the sermon, blocking off escape routes from the area by blowing up cars and leaving the burning wrecks blocking the roads, police reports said.

No one claimed responsibility immediately following the attack, but Daesh has targeted Sufis in the area in the past.