The way the prosecutor described the attack is more reminiscent of a military assault than an incident of terrorism.

Some astonishing revelations from the Egyptian state prosecutor on the mosque attack in the Sinai that killed 305 people and wounded more than a hundred.

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.

The attackers were not fanatical suicide bombers. This was, from start to finish, a military operation, extremely well organized, well funded, and absolutely cold blooded. They not only killed everyone in the mosque, they tried to kill anyone who was running away. The objective to strike terror in the Egyptian people appears to have been secondary to eliminating a mosque whose very existence was an affront to ISIS and killing "infidels."

The Egyptian military tried to retaliate with a conventional bombing attack but found few targets.

The Times of Israel reports that ISIS is also at war with local Beduin tribes in the Sinai:

The pretext for Friday’s attack was likely the mosque’s affiliation with Islam’s mystical Sufi stream. It is known as the birthplace of Sheikh Eid al-Jariri, considered the founder of Sufism in the Sinai. The Islamic State, like al-Qaeda and other radical Sunni organizations before it, has denounced the Sufis. But for IS it isn’t merely about religious differences: In the past two years, the Sufis have worked in tight cooperation with Egyptian security forces in the peninsula in an effort to counter the Islamic State and curb recruitment among the local Beduin. Recent months have also seen a clan war that has pitted several tribes (notably Tarabin) against the Islamic State. The spate of mutual killings, which has included beheadings (not only on the part of IS), may also be connected to Friday’s attack. Last May, tribesmen executed eight Sinai Province operatives in retribution for a car bomb the terror group detonated near a Tarabin encampment. Among the triggers for those incidents was Sinai Province’s effort to take control of smuggling along the border with the Gaza Strip and to stem the flow of cigarettes, which they forbid, into the Sinai. Those restrictions threatened the livelihood of the Tarabins, who responded with violence.

We saw this same kind of tribal warfare against ISIS in Iraq, with the terrorists exacting revenge on Shias and some Sunni tribes who were cooperating with the government. This could mean that in Egypt, the fighting is likely to get even bloodier.

The military assault on the mosque shows that ISIS is far from finished in the region. Being able to marshall 30 terrorists and purchase 5 SUV's as well as weapons and ammunition bespeaks an organization growing in strength. Today, most ISIS attacks are confined to the Sinai. But it's only a matter of time before they start shooting up popular tourist spots and other places were westerners gather.