IS retains territory in the desert plains along the Iraqi frontier despite losing the vast bulk of its cross-border "caliphate" to various military offensives.

The senior Iraqi official said Baghdadi was in the Hajin, Shaddadi, Suwar and Markadah areas and "travels accompanied by four or five people, including his son and son-in-law".

"His movements are discreet and he never travels in a convoy," the official said on condition of anonymity.

Originally from Iraq, Baghdadi has been dubbed the "most wanted man on the planet" and the United States is offering a $25 million reward for his capture.

The intelligence official said the noose was closing around the jihadist leader after Iraqi forces captured five top IS commanders in an unprecedented raid into war-torn Syria on March 24.

"Officers from Iraqi intelligence entered Syrian territory and gained access to the zones controlled by IS," he said.

The five men had featured in IS execution videos filmed while the group ruled over vast swathes of Iraq, the official said.

One of those detained, former Syrian anti-government fighter Saddam al-Jamal, allegedly confessed to Iraqi forces that he had supplied IS with arms stolen from the Syrian army.

The official said 39 IS fighters had been killed in cross-border air raids by Iraqi forces in Syria over the past few weeks and that the group had seen a "sharp decrease" in numbers.

Iraq's interior ministry said in February that Baghdadi was being treated at a field hospital for wounds sustained in an earlier air strike.

In mid-2017, Russia said it had probably killed Baghdadi in a late May air raid near Raqa in Syria, but later said it was still trying to verify his fate.

In September, an American military chief said the jihadist chief was still alive and probably hiding in eastern Syria's Euphrates Valley.