One of the most wanted leaders of an Al-Qaeda-linked group operating in Iraq and Syria had been held in detention for five years but was released in 2010, an Iraqi official revealed Sunday.

Abu Mohammed al-Adnani, spokesman for the Islamic State of Iraq and the Levant (ISIL) militant group, was detained by international forces in Iraq in May 2005, the senior intelligence official told AFP.

He did not specify why he was freed.

At the time of his arrest, he used the name "Yasir Khalaf Hussein Nazal al-Rawi", and now goes by various others such as "Abu Mohammed al-Adnani Taha al-Banshi", "Jabr Taha Falah", "Abu al-Khattab" and "Abu Sadeq al-Rawi", the official said.

Adnani was born in 1977 and lived in the Haditha district of Anbar province in western Iraq, the official said, adding that his mother's name was Khadija Hamed.

He is considered one of the main leaders of ISIL, a jihadist group which carries out attacks inside Iraq and is also fighting alongside rebel forces in Syria against President Bashar al-Assad's troops, and has released audio recordings and written statements on behalf of the militant group.