JEDDAH, Saudi Arabia (AFP) - The world's top Islamic body denounced on Monday the persecution of Christians in Iraq's second city Mosul as an "intolerable crime", and offered to help those displaced by a jihadist offensive.

Organisation of Islamic Cooperation secretary general Iyad Madani said the "forced displacement" of Mosul's Christians showed the IS's "practices have nothing to do with Islam and its principles that call for tolerance and co-existence".

"These atrocities also contradict the principles of the OIC," of which Iraq is a member, Mr Madani added, noting that the body was "ready to provide the necessary humanitarian assistance to displaced persons until they be able to return to their homes".

At the weekend, hundreds of families fled Mosul, abandoning homes and belongings after IS fighters running the city issued an ultimatum for Christians to convert, pay a special tax, leave or face execution.

Families who were forced on the road and leaders of Iraq's Chaldean and other churches said Mosul was now emptied of Christians for the first time in history.

Jihadist fighters want to create a state based on an extreme interpretation of sharia - or Islamic law - and have targeted all minorities in the Mosul area.