"What is happening is an attempt to stop us from our efforts in the fight against terrorism, to destroy our efforts to stop the awful criminal plan that aims to destroy what is left of our region", Egypt's President Abdel Fattah el-Sisi said.
"I am deeply saddened by the cowardly terrorist act that targeted a mosque, in northern Sinai, and resulting deaths and injuries, the Crown Prince said".
After an explosion, gunmen who were waiting outside the mosque opened fire at worshipers as they fled Friday prayers, Ahram Online said.
In a statement afterward, el-Sissi said the attack "will not go unpunished" and that Egypt will persevere with its war on terrorism.
The conflict has killed hundreds of soldiers and militants over the years, although journalists are banned from the area and exact numbers are unclear. Numerous attacks have killed many throughout the country.
Such an evil and cowardly terrorist attack on worshipers in Egypt.
Eyewitnesses reported ambulances ferrying casualties from the scene to nearby hospitals after the Al Rawdah mosque in Bir al-Abed, west of Arish city, was targeted.
The jihadists have also attacked local tribes and their militias, branding them traitors for working with the army and police. Islamic militants, including the local affiliate of the Islamic State group, consider Sufis heretics due to their less literal interpretations of the faith.
MENA also said a state of emergency had been declared in Sinai.
Egypt has also faced attacks by militants in its Western Desert, including an attack last month that killed 16 police, according to an official tally issued by the Interior Ministry.
Appalled by the sickening attack on a mosque in North Sinai.
During Palm Sunday of April 2017 ISIL-SP carried out two suicide attacks against the Christian minority of Egypt. St. George's Church in Tanta and Saint Mark's Coptic Orthodox Cathedral in Alexandria were attacked, leaving 45 people dead and 126 people injured.