Updated

The mosque attack in Egypt's Sinai by some two-dozen heavily armed Islamic militants on Friday which killed over 300 people was built by a prominent Sufi figure. A large portion of the area's Bedouin population adheres to Sufism, a mystical movement within Islam with followers across most of the Muslim world.

The link between Sufism and the attack has raised questions about the Sufis and why the militants chose to targeted them.

Here are five things you need to know about Sufism and its followers in Egypt:

ORDERS

Sufism is a mystical form of Islam considered an integral part of the faith by its followers. They belong to "turuq," Arabic for orders, which are founded by masters who trace their learnings to the teachings of the Prophet Muhammad.

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15 MILLION

Egypt has millions of Sufi followers, with the unofficial figure estimated to be around 15 million in the country. They follow over 17 orders or methods.

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SHRINES

Shrines of Sufi saints are found across the country and celebrations of their saints' birthdays are very popular, drawing millions of Egyptians.

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CAUGHT IN POLITICAL CROSSFIRE

Though they shun politics and worldly matters, Sufis are constantly under attack by the ultraconservative Salafis who consider them heretics and condemn their "innovations" or rituals. The customarily bearded Salafis have carried out a series of attacks against Sufi shrines, driving Sufi leaders to close ranks with government and anti-Islamists. They heavily supported the removal of Islamist President Mohammed Morsi in 2013 and threw their support behind the army chief-turned-president Abdel-Fattah el-Sissi's crackdown on Islamists.

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OPEN TO ALL

Not a sect, there are Sufi Sunnis and Shiites. Mosques named after Sufi saints and masters are attended by all Muslims.