"I am disgusted by the evil attack that killed & injured so many Egyptians in Sinai today".
In March 19 2016 13 Egyptians policemen were killed by ISIL-SP during an attack in the El-Arish checkpoint, Arish is the largest city in Sinai.
U.S. President Donald Trump, in a post on Twitter on Friday, called the assault a "horrible and cowardly terrorist attack".
Arabiya news channel and some local sources said some of the worshippers were Sufis, whom groups such as Islamic State consider targets because they revere saints and shrines, which for Islamists is tantamount to idolatry.
Police officers told the Associated Press that men in four off-road vehicles shot at worshipers who were at the al-Rawdah mosque for Friday prayers. Officials said a midair explosion of a Russian jet in 2015 over the Sinai was the work of terrorists.
"The world can not tolerate terrorism, we must defeat them militarily and discredit the extremist ideology that forms the basis of their existence!", he wrote.
The attack started when an explosive went off in a building adjacent to the mosque, and gunmen fired at worshippers as they fled, eyewitnesses told CNN.
Dozens Of People Are Reported To Have Died In A Huge Attack On A Mosque In Egypt
El-Sisi said that the military and police "will avenge our martyrs" and will respond "using brute force against those fragments of terrorists" in the coming period to ensure stability and security.
Security has always been one of the key sources of public support for the former general, who is expected to run for re-election for another four-year term early next year. Citing official sources, state-run MENA reported that the mosque is largely attended by Sufi Muslims - a form of Islam considered heretical by some conservatives and extremists like the Islamic State group.
The Islamic group Ansar Bait al-Maqdis [Supporters of the Holy House], that placed Jerusalem as its' focus, carried out a large attack in October 24 2014 in the Bedouin town of Sheikh Zuweid.
The startling bloodshed, which also wounded at least 109, was the latest sign of how more than three years of fighting in Sinai has been unable to crush an insurgency waged by the IS affiliate.
There have been a wave of attacks on the country's Coptic Christian minority, but attacks on mosques are rare in Egypt.
President Trump used the massacre at a mosque in Egypt to renew his calls for a travel ban and "wall" on Friday afternoon.