At least 235 worshippers were killed Friday in an attack by Islamist militants on a Sufi mosque in the town of Bir al-Abed in Egypt’s Sinai Peninsula. Another 109 people were injured in what the Egyptian government has declared to be the deadliest terrorist attack in the country’s modern history.

The attack began when a possible suicide bomb was detonated inside the mosque just as afternoon Friday Prayers were finishing. As people fled the mosque they were fired on by masked men in pickup trucks. Vehicles had been set on fire to keep anyone from escaping. When ambulances arrived on the scene to tend to the dead and wounded, the gunmen opened fire on the paramedics, dramatically increasing the number of casualties.

In a televised address shortly after an emergency meeting with his cabinet ministers, Egyptian President Gen. Abdel Fatah al-Sisi promised a swift response against those responsible for the attack. “The armed forces and the police will avenge our martyrs and restore security and stability with the utmost force,” Sisi declared.

Several hours later, Egyptian jetfighters descended on the mountains surrounding Bir al-Abed purportedly killing an unspecified number of fighters and destroying the vehicles used the attack.

The government also announced that in response to the attack it would be delaying the opening of the Rafah border crossing between the Sinai and the Gaza Strip. The crossing would have been open Saturday through Monday to allow crucial supplies into what is effectively an open-air prison for Palestinians maintained by Israel in conjunction with the Egyptian dictatorship.

While no group has claimed responsibility for the attack, it is likely to have been carried out by Sunni militants loyal to the Islamic State of Iraq and Syria (ISIS), who view Sufi Muslims as apostates.

An Islamist insurgency has been underway in the Sinai since 2013 when Egyptian President Mohammed Mursi was ousted in the military coup that brought Sisi to power. Until recently attacks had been mostly limited to military targets, check points and troop convoys.

The Sinai, a largely desert area that has a limited military presence, was used as a transit point for Islamist militants and weapons being funneled from Libya and Tunisia into Syria as part of the US effort to overthrow the Russian- and Iranian-backed Assad government.

With the official defeat of ISIS in Iraq and Syria, many of the foreign fighters are now returning to the Sinai and the wider region across North Africa.

Ansar Beit al-Maqdis, a Sunni Islamist militia which has been waging an insurgency against the Egyptian military in the Sinai, pledged allegiance to ISIS in 2014. The group claimed responsibility for the 2015 bombing of a Russian passenger jet which was flying out of the resort town of Sharm El Sheikh, killing all 224 onboard.

A commander of the group declared in January that they would eradicate Sufis living in the Sinai, including in the area where Friday’s attack took place. An elderly Sufi cleric was executed by the ISIS affiliate in late 2016 and Sufi shires have been targeted for destruction.

Other Islamist militias active in the Sinai include Ansar al-Islam,0 a group which has purported ties to Al-Qaeda.

The attack brought perfunctory condemnations and words of support for the military dictatorship in Cairo from leaders around the world.

While sending his condolences US President Donald Trump used the opportunity to push for an expansion of the imperialist wars already being waged by the US in the Middle East and across Africa under the threadbare pretext of the so-called war on terror. “The world cannot tolerate terrorism, we must defeat them militarily and discredit the extremist ideology that forms the basis of their existence!” the president tweeted.

He followed up with a tweet which exploited the attack to push his reactionary anti-immigrant and anti-Muslim agenda. “We have to get TOUGHER AND SMARTER than ever before, and we will. Need the WALL, need the BAN! God bless the people of Egypt.”