On Tuesday, Grand Mufti Shawqi Allam labelled the ISIL militants as members of a corrupt and extremist organization.
He said the group poses a danger to Islam and Muslims, tarnishes the image of Islam, sheds Muslims’ blood and spreads corruption.
The mufti further noted that fighting terrorism requires international and regional cooperation at all levels.
On Sunday, Iraq’s human rights minister said the ISIL had executed at least 500 Izadi Kurds after seizing the town of Sinjar, situated 404 kilometers (250 miles) northwest of the capital Baghdad, more than a week ago.
Mohammed Shia al-Sudani said ISIL militants burned alive some of their victims, including women and children.
Reports say the Takfiri group has also kidnapped hundreds as slaves across some militancy-riddled regions.
United Nations’ rights monitors have called for urgent international action to avoid a potential genocide of Izadi Kurds in northern Iraq within days.
The UN monitors say thousands of the Kurdish minority are at risk of death either by violence or hunger and thirst.
"All possible measures must be taken urgently to avoid a mass atrocity and potential genocide within days or hours," said Rita Izsak, the UN's minority rights expert.
Thousands of members of Izadi Kurds have been trapped in mountains surrounding Sinjar ever since the town fell into the hands of ISIL terrorists.