The Islamic State terror organisation chief Abu Bakr al-Baghdadi is reported to have abandoned Mosul, leaving local commanders behind to continue the battle.
With Iraqi troops making steady progress in their assault to retake Mosul from the jihadists, a US defence official said Baghdadi had fled to avoid being trapped inside.
It was the latest sign that IS is feeling the pressure from twin US-backed offensives that have seen it lose much of the territory it once controlled in Iraq and Syria.
Speaking to reporters in Washington, the defence official said Baghdadi had left Mosul before Iraqi forces seized control of a key road at the beginning of March, isolating the jihadists in the city.
“He was in Mosul at some point before the offensive....He left before we isolated Mosul and Tal Afar," a town to the west, the official said. "He probably gave broad strategic guidance and has left it to battlefield commanders."
Baghdadi, who declared IS's cross-border "caliphate" at a Mosul mosque in 2014, in an audio message in November urged supporters to make a stand in the city rather than "retreating in shame".
Iraq launched the offensive to retake Mosul -- which involves tens of thousands of soldiers, police and allied militia fighters -- in October. After recapturing its eastern side, the forces set their sights on the city's smaller but more densely populated west.
In recent days Iraqi forces have retaken a series of neighbourhoods in west Mosul as well as the provincial government headquarters and a museum where IS militants filmed themselves destroying priceless artefacts.
The military said on Wednesday they had also taken the infamous Badush prison northwest of Mosul where IS reportedly executed hundreds of people and held captured Yazidi women.
Iraqi forces were on Thursday "combing the city center area to defuse (bombs in) homes and shops and buildings," Lieutenant Colonel Abdulamir al-Mohammedawi of Iraq's elite Rapid Response Division told AFP.
Forces were also "searching for snipers in the city centre," Mohammedawi said. The area is located on the edge of Mosul's Old City, a warren of narrow streets and closely spaced houses that could see some of the toughest fighting of the battle.
"Currently there is no order from the operations command to advance toward the Old City. We will advance when this order is issued," Mohammedawi said.
Hundreds of thousands of civilians are believed to still be trapped under IS rule in Mosul. Those who did manage to escape the city said the jihadists were growing increasingly desperate.
(With inputs from PTI)
