Egypt's religious institute "Dar El-Eftaa El-Masreya" condemned on Monday the killing of Sufi Sheikh Sulaiman Abou Harraz of El-Sawarka tribe in North Sinai by the Ansar Beit Al-Maqdis terrorist group, calling it a "terrible crime."

The observatory said in a statement that this "terrorist crime against a man who exceeded 100 years of age represents nothing less than the heinous and bloody behavior of a terrorist organisation, which pledged allegiance to the Islamic State in Iraq and Syria, violating the main principles of Islam."

Harraz, a revered Sufi cleric and Sinai tribal elder, was taken by the Ansar Beit Al-Maqdis group from in front of his house in Arish city under gun threat.

The IS-affiliated Islamist militant group in Egypt released images purporting to show the execution of Harraz on Saturday.

It accused the elderly sheikh of ''practicing witchcraft."

Ansar Beit Al-Maqdis has claimed responsibility for most of the attacks against security personnel and installations in North Sinai since 2013.

The group has carried out dozens of executions against Sinai civilians who it accused of cooperating with security forces.

A decade-long Islamist militant insurgency in the northern part of Sinai peninsula has intensified over the past years, following the ouster of Islamist president Mohamed Morsi in 2013.