Another 128 people were injured, according to a statement from the public prosecutor read out on Egyptian state-run news channel Nile TV.
The prosecutor also gave more detail about how the brutal attack unfolded. The attackers arrived in five SUVs and were armed with automatic machine guns, the statement said. They took position in front of the mosque and its entrances.
Survivors of the incident now at the hospital described massive gunfire and loud explosions at the start of the attack. A number of attackers, some of them masked, then entered the mosque, the statement said.
The attackers had long beards and hair, were wearing military fatigues and were armed with heavy machine guns, according to the statement. One of those who entered the mosque was carrying an ISIS flag, it said.
There has not yet been a claim of responsibility from ISIS or its affiliate in Egypt. However, the attack bears the hallmarks of a strike by ISIS.
Despite the efforts of Egyptian security forces, ISIS maintains a foothold in the north of the Sinai Peninsula and inspires local Islamist extremist groups.
Victims are seen on the floor of al Rawdah mosque following the gun and bomb attack Friday.
President vows ‘brute force’
President Abdel Fattah el-Sisi has vowed to respond to the massacre — believed to be the deadliest terror attack on the country’s soil — with “brute force.”
Egyptian warplanes conducted airstrikes on “terrorist outposts” and vehicles following the attack, the military said Saturday.
“The Egyptian Air Force pursued the terrorist elements, discovered and destroyed a number of vehicles that carried out the brutal terrorist killings, and killed all terrorists inside those vehicles,” military spokesman Tamer Rifai said in a statement Saturday.
It also targeted a number of terrorist outposts containing weapons, ammunition and radical elements, Rifai said.
A teenage survivor of the attack is treated at a hospital in Ismailia on Friday.
Al Rawdah mosque is known as the birthplace of an important Sufi cleric. Sufism is a mystical branch of Islam that some jihadists consider heretical.
Witnesses told CNN Friday that the attack started when an explosive device went off in a building adjacent to the mosque and that gunmen fired at worshippers as they fled. They said gunmen then entered the mosque and fired at those inside.
The attackers had also set up “ambush” locations and opened fire on ambulances as they transported the wounded to al-Arish before the arrival of security services, according to witnesses.
Photos from inside the mosque showed what appeared to be bodies lined up in rows on the carpet.
One man told CNN he drove one of the first ambulances to the scene but turned around after shots were fired at the vehicle. Ambulances from al-Arish managed to reach the mosque only after security forces secured the road, he said.
The attackers used automatic weapons, said Diaa Rashwan, the chairman of the state information service. Some victims were also killed by the explosions.
In a short, televised speech after meeting with security officials, Sisi said the government would hunt down the attackers.
“We will respond to this act with brute force against these terrorists,” he said.
“This terrorist act will strengthen our resolve, steadfastness and will to stand up to, resist and battle against terrorism.”
President Abdel Fattah el-Sisi, center, meets with officials in Cairo after the mosque attack.
Three days of national mourning have been declared. Sisi has also ordered the armed forces to build a memorial to those killed at the mosque, a statement on his official Facebook page said.
The grand imam of Al-Azhar, the premier religious authority in Egypt, condemned the “barbaric attack” on the mosque.
“The shedding of blood, the violation of the sacred houses of God and the terrorizing of worshippers, are acts of corruption on the earth,” Ahmed El-Tayyeb said.
The targeting of mosques followed an attack on churches
, El-Tayyeb said, adding that Egyptians would prevail over terrorism with solidarity and determination.
Northern Sinai unrest
Friday’s attack prompted wide international condemnation, with US President Donald Trump among the leaders expressing their condolences and vowing to continue the fight against terrorism.
Sisi expressed concern recently that ISIS militants fleeing Iraq and Syria would come to Egypt.
Egyptian security forces face almost daily attacks from militants with ISIS ties in northern Sinai.
The Wilayat Sinai group, which pledged allegiance to ISIS in 2014, has been behind numerous attacks and hundreds of deaths in the desert region.
CNN’s Ian Lee, Abeer Salman, Hilary McGann, Saskya Vandoorne, Schams Elwazer, Sarah El Sirgany, Joe Sterling, Steve Almasy and journalist Jacob Wirtschafter contributed to this report.