ISIL's leader Abu Bakr al-Baghdadi is alive and being treated at a medical facility in northeastern Syria after being severely wounded in an air raid, a senior Iraqi official said.

The head of Islamic State of Iraq and the Levant (ISIL, also known as ISIS) sustained serious wounds to his legs during air raids, Abu Ali al-Basri, Iraq's intelligence and counterterrorism department chief, was quoted on Monday by the government-run al-Sabah daily as saying.

"We have irrefutable information and documents from sources within the terrorist organisation that al-Baghdadi is still alive and hiding with the help of his collaborators," al-Basri said.

Al-Baghdadi - one of the world's most-wanted men with a $25m US bounty on his head - is currently in Syria's Jazeera desert, west of Deir Az Zor, he said.

He suffers from "injuries, diabetes and fractures to the body and legs that prevent him from walking without assistance", said al-Basri.

Despite a series of major military defeats over the past year, ISIL retains a significant presence in northeastern Syria's Hasakah province despite having lost most of its cross-border "caliphate", which al-Baghdadi announced in 2014 after his fighters' shocking military victories across the region.

It was unclear what air force was responsible for targeting ISIL's leader.

Al-Basri was quoted as saying he was wounded during air raids in Iraq.

Russia's defence ministry has said it may have killed al-Baghdadi in one of its air raids on the outskirts of Syria's Raqqa, an ISIL stronghold, until the group was ousted from the city late last year.

American broadcaster CNN on Monday quoted US officials as saying that al-Baghdadi was wounded in Raqqa and forced to relinquish command of the armed group because of his injuries.

"There have been isolated strikes by Russians in Raqqa, but as there's no timeline to it, we don't know if it's ours," an unidentified American official said of the attack that wounded the ISIL chief.

Another US official told the network it was unclear if he was again leading the group. "I do not know how much Baghdadi is day-to-day running the shop."