Story highlights Between 25 and 30 armed men carried out the attack, officials say

At least one attacker carried ISIS flag

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(CNN) Dozens of men wearing military combat uniforms and armed with automatic machine guns carried out the deadly assault on a Sufi mosque in northern Sinai, Egyptian authorities said.

Twenty-five to 30 attackers arrived in five SUVs at the al Rawdah Sufi mosque in Bir al-Abed on Friday. Some wore masks and at least one was carrying an ISIS flag, the state prosecutor told state-run Nile TV in a statement.

They positioned themselves at the building's entrances and the front of the mosque shortly before the massive gunfire and loud explosions rang out.

By the time the attackers' weapons went quiet, 305 people were dead, including 27 children, the prosecutor said Saturday. An additional 128 people were wounded.

The al Rawdah Sufi mosque is known as the birthplace of an important Sufi cleric. Sufism is a mystical branch of Islam that some jihadists consider heretical.

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