Iraqi soldiers hold a position on the frontline on the outskirts of the Kurdish-controlled area of Makhmur, some 60 kilometres (35 miles) south of Mosul, on July 17, 2016.

Many ISIS leaders have fled Mosul with their families towards Syria ahead of a planned offensive by US-backed Iraqi forces on the city, Iraq’s defence minister said on Saturday.

Khaled al-Obeidi said he had intelligence of increasing conflict, especially over financial issues, among ultra-hardline militants of the group known as Daesh in Arabic by its enemies.

“Many Daesh families and leaders in Mosul have sold their property and sneaked out towards Syria, and a segment even tried to sneak out towards (Iraq’s Kurdish) region”, he said in an interview on state television.

ISIS has lost at least half the territory it seized in Iraq in 2014. The group has also lost territory in Syria, where it emerged amid a civil war which is now in its sixth year, but US-backed rebel forces there have had less success in beating it back.

Fighters in Mosul, the group’s de facto capital in Iraq and the largest city under its control anywhere across its self-proclaimed caliphate, are thought to number in the thousands but probably under 10,000.

Iraq is expected to mobilise up to 30,000 forces to retake the city in coordination with US-led coalition air support.

The campaign has gained momentum in recent weeks after government forces restored Falluja and retook a key air base south of Mosul, though some officials still question whether the military will be ready and what will happen in Mosul after ISIS is removed.

Obeidi said the biggest challenge will be protecting civilians, who he said number around 2 million.

“We expect when operations begin in the city proper there will be large displacement. The smallest number we are expecting is about half a million people,” Obeidi said.

The International Committee for the Red Cross says up to 1 million people could be driven from their homes in Mosul, and the United Nations estimates the number could be even higher.

Ten million Iraqis already require assistance, including more than 3 million who have been internally displaced – about one-tenth of the population.

Related articles across the web

• Iraqi Army Claims to Have Captured Last Fallujah Neighborhood Held by ISIS
• Iraqi forces retake Islamic State holdout in Fallujah
• Iraq is getting close to an assault on ISIS' biggest stronghold
• UNHCR warns of Iraq funding crunch as thousands flee Falluja
• Iraqi army closes in on IS militants near Falluja
• Isis video shows US-led coalition killing 250 jihadists in single air strike
• ISIS director of Hawija Hospital flees towards Mosul
• U.S. Official Sees Progress Against Islamic State, War Continuing
• Thousands displaced from Fallujah says Iraqi official
• Iraqi children 'relentlessly targeted' as war rages on, UNICEF warns