Islamic State (IS) group leader Abu Bakr al-Baghdadi has fled the besieged Iraqi city of Mosul and is believed to have delegated tactical control of the battle to local commanders, a US defence official said Wednesday.

The official said the elusive leader, who last appeared in public in Mosul in July 2014 to proclaim a "caliphate", fled the former IS group bastion some time before Iraqi security forces surrounded the city.

"He was in Mosul at some point before the offensive. We know he's been there," the official told reporters. "He left before we isolated Mosul and Tal Afar," a town to the west of the city.

Baghdadi is not believed to be exercising any kind of tactical influence on how the Mosul fight will play out, the official said. "He probably gave broad strategic guidance and has left it to battlefield commanders."

Some in Mosul said the fact that al-Baghdadi has fled is an indication that victory is near for the Iraqi forces fighting in Mosul.

FRANCE 24’s Gallagher Fenwick cited Mosul residents as saying that Baghdadi’s departure shows that he is “no honourable leader and rather a coward, because he chose to leave his troops behind – who are facing defeat – rather than engage in combat alongside his troops”.

The hunt for Baghdadi is being led by various groups, including US special operations forces, while the anti-IS group coalition focuses on killing battlefield commanders.

Rumours have abounded in recent months about the Iraqi jihadist leader's health and movements. His militant group has lost most of the land it once held in Iraq and Syria but hopes to cling to scraps of its self-declared caliphate, the official said.

The jihadists held the most territory in summer 2014, just before the US-led coalition launched its offensive on the group. Since then they have lost 65 percent of the land they'd seized across much of northern Syria and large parts of Iraq.

Raqqa 'not the final battle'

The IS group is now looking beyond the seemingly inevitable loss of its strongholds of Mosul in Iraq and Raqqa in Syria.

"I don't think they have given up on their vision of their caliphate yet," the Pentagon official said, noting that the jihadists hope to hold on to parts of eastern Syria and western Iraq.

"They still believe they can function and are still making plans to continue to function as a pseudo-state centred in the Euphrates river valley."

Iraqi security forces, backed by Western air power, have recaptured the eastern part of Mosul and are making gradual progress into the western side.

IS group militants realise their days are numbered in Mosul, the US official said. And despite having spent two years building up their defences in Raqqa, they know they will lose that bastion too.

"Logically, any of those leaders would look at that situation and say from a military perspective this may be not be tenable for us to hold," the official said.

"Raqqa would probably not be the final battle against ISIS," he said, referring to the group by another acronym. "There is still ISIS in the rest of the Euphrates river valley downstream that will have to be dealt with."

About 15,000 IS group fighters remain, including some 2,500 in Mosul and neighbouring Tal Afar and as many as 4,000 still in Raqqa, the official said.

by France24