CAIRO (TNS) — At least 235 people were killed and scores more injured when gunmen stormed a mosque in Egypt's Sinai Peninsula, setting off explosives and firing on worshippers during Friday prayers, authorities said.

There was no immediate claim of responsibility for the assault in the town of Bir Abd, about 25 miles from the North Sinai provincial capital of Arish. But the region has long been the scene of a simmering Islamist insurgency, and Islamic State fighters have dramatically escalated the level of violence there in recent years.

Friday's attack targeted a mosque frequented by Sufis, a mystical sect viewed as infidels by Islamic State and other Sunni Muslim extremists.

The assailants opened fire on worshippers from four off-road vehicles and blocked escape routes from the area by blowing up cars on the roads, local police officers told The Associated Press.

In addition to the 235 killed, more than 100 were injured, according to state-run television. Egypt's presidency declared three days of national mourning.

A video taken from inside the mosque showed the grim aftermath of the attack. Dozens of bodies were arrayed on the carpeted floor, their arms folded and their faces covered in sheets, many of them streaked with blood.

Activists on Facebook issued pleas for blood donors to make their way to the Beer Abed hospital, where many of the wounded were taken.

Hussam Rifaii, a parliamentary member from Arish, told the local Masrawy media outlet that most of the casualties were from the Sawarkah tribe, Sufis who are seen as widely supportive of the government, and who have refused to cooperate with Islamic State.

The group has targeted both Sufis and their shrines in the past. Almost a year ago, Islamic State published a video depicting the beheading of Suleiman Abu Haraz, the 98-year-old spiritual leader of the Sufis in the Sinai who had been kidnapped from his house in the city of Arish.

Islamist militants have stepped up attacks in Sinai since Egypt's military overthrew the country's Islamist president, Mohamed Morsi, amid a wave of anti-government protests in 2013.

Hundreds of police, soldiers and civilians have been killed since then, most of them in attacks carried out by fighters loyal to Islamic State, who consider Sinai one of the provinces of the group's self-proclaimed caliphate. The 47-mile stretch of road connecting Arish to Beer Abed has become a regular escape route for the militants.

Although Islamic State has lost control of most of the territory it once held in Syria and Iraq, security experts have warned that the group remains active in other parts of the world, and its followers likely will revert to guerrilla-style tactics.

(Los Angeles Times staff writer Zavis reported from Beirut, and special correspondents Medhat and Bulos reported from Cairo and Dubai, respectively.)