CAIRO — Militants set off a blast and gunned down fleeing worshippers at crowded mosque in Egypt’s northern Sinai Peninsula on Friday, killing at least 235 people in what appeared to mark the deadliest single assault on Egyptian civilians by suspected Islamist extremists.

There was no immediate claim of responsibility for the attack on the mosque – which is often frequented by Sufi Muslims – where an apparent suicide bombing ripped across the facade and people were shot as they tried to scramble to safety.

Egyptian security forces have struggled for years against an Islamic State affiliate based in the Sinai Peninsula that has killed hundreds of police and military personnel in an insurgency against the government of President Abdel-Fattah el-Sissi.

The mosque death toll, reported by state media, could not be independently confirmed. Yet Egyptians were already mourning it as the biggest loss of life from a militant attack in decades – surpassing the number of dead in the downing of a Russian airliner over Sinai in 2015 believed carried out by Islamic State-linked militants.

Islamist attacks have targeted Copic Christian churches in the past, but strikes against mosques have been rare. Many Sunni Muslim militant factions consider Sufism, a mystical branch of Islam, to be heretical.

The bloodshed at the Rawda mosque, near the town of Bir al-Abd, also took place in an area dotted with security outposts, underscoring the ability of militants to strike at the heart of government-protected zones.

The attack had the hallmarks of a highly coordinated operation. Militants who arrived at the mosque in several four-wheel-drive vehicles, according to Egypt’s ambulance authority. Bombs were detonated at the mosque, and as worshipers fled, they were gunned down by the militants, the authority said.

But further details remained unclear on the motives for the attack, including the number of assailants and why the mosque was targeted.

Dozens of bodies covered with blankets or bloodied sheets, laid in rows inside the mosque. Some of the injured were ferried away in cars and in the beds of pickup trucks.

Tarek Eldewiry, a 22-year old resident of Bir al-Abd who was not present during the attack but spoke to injured friends and neighbors afterward, said the assault started with an explosion outside the mosque after the first Friday sermon.

“When the people ran outside, a number of gunmen started shooting randomly at everyone.” Some survived by running back inside the mosque, he said.

The mosque would have been packed. It was frequented by the town’s residents, and on a Friday, travelers on the road often stopped to pray there, he said.

“Horrible and cowardly terrorist attack on innocent and defenseless worshipers in Egypt,” wrote President Donald Trump in a tweet. “The world cannot tolerate terrorism, we must defeat them militarily and discredit the extremist ideology that forms the basis of their existence!”

Egypt’s insurgency gathered momentum after a military coup in 2013 that ousted Mohammed Morsi, Egypt’s first democratically elected president and a leader of the Islamist Muslim Brotherhood.

The militants have repeatedly mounted large-scale, complex attacks on security personnel. Since July 2013, at least 1,000 members of the security forces have been killed in attacks in Sinai, according to data compiled by the Tahrir Institute for Middle East Policy.

Assaults on civilians – like Friday’s mosque siege – have been more rare. The Islamic State affiliate in Egypt, called Wilayat Sinai, had previously claimed responsibility for the downing of a Russian airliner over Sinai in October 2015 that killed all 224 people on board. The militants have also increasingly targeted Egypt’s Coptic Christian minority, as well as Sufi Muslims, considered heretics by the Islamic State.

Sinai remains one of the lingering strongholds for the Islamic State as the group’s self-proclaimed caliphate in Syrian and Iraq has all but collapsed under air and ground attacks.

Last year, militants in Egypt claiming affiliation with the Islamic State asserted responsibility for two beheadings near Arish, including an elderly cleric, identified as Sulaiman Abu Haraz, who was believed to have ties to the area’s Sufi followers.

Fahim reported from Istanbul.

This photo released by Egypt’s Presidency shows Abdel-Fattah El-Sissi, center, meeting with officials in Cairo after militants attacked a crowded mosque during Friday prayers in the Sinai Peninsula. The attackers set off explosives, spraying worshippers with gunfire and killing at least 184 people in the deadliest ever attack on Egyptian civilians by Islamic extremists. (Egyptian Presidency via AP) (AP)