Tikrit: Iraq’s military backed by air strikes from a US-led coalition on Thursday seized the centre of Shirqat, a northern town seen as a stepping stone in the campaign to recapture Mosul from Daesh.

The army, backed by local police and tribal fighters, were still clashing with the ultra-hardline terrorists after taking control of the mayor’s office, the municipal building and the hospital, said a source from the Salahuddin Operations Command, which oversees military operations in the area.

Shirqat, on the Tigris river 100km south of Mosul, has been surrounded by Iraqi troops and Iranian-backed militias allied to the government but the militias so far have not participated in the operation.

Iraqi forces have advanced swiftly through the Shirqat area since Prime Minister Haider Al Abadi announced the operation on Tuesday morning.

The town’s proximity to Iraqi supply lines reaching Qayyara airbase further north, which will be used as a logistics hub for the push on Mosul, lends it strategic importance.

Remaining Daesh fighters in Shirqat are resisting in groups of three and four from inside houses, according to the Iraqi operations command source, who said three army personnel had been killed in recent hours.

Tens of thousands of civilians were thought to be trapped in the area, which has been under Daesh control since the group seized a third of Iraqi territory in 2014. But the operation has not generated the large-scale displacement seen in other recent campaigns.

US and Iraqi officials have said the push on Mosul could begin in October, though there are concerns that not enough planning has been done for how to manage the city, Iraq’s second-largest, if and when Daesh is expelled.

Hawija, east of Shirqat, is the other remaining Daesh bastion south of Mosul. The group also controls the city of Tel Afar, west of Mosul towards the Syrian border.

In New York, the US envoy to the anti-Daesh coalition said on Wednesday there would be “no tolerance” for sectarian torture and other abuses resulting from the planned offensive to recapture the group’s de facto Iraqi capital of Mosul.

Brett McGurk, speaking at a meeting on the sidelines of the annual UN gathering of world leaders, said the coalition was already taking steps to ensure there would be no repeat of the abuses seen in the wake of the recapture of Iraq’s Fallujah in June, when Shiite militias detained, abused and tortured scores of Sunni civilians. Improved screening of people fleeing the city was crucial, he said, to ensure that ordinary residents received assistance and did not face abuses.

“We must make sure the screening process in Mosul is done professionally with some third-party observers at the screening centres, that is what we hope to have,” McGurk told the meeting.

With a population at one time as large as two million, mostly Sunni, Mosul is the largest urban centre under the ultra-hardline militants’s control. Its fall would mark their effective defeat in Iraq, according to Iraqi Prime Minister Haider Al Abadi.

Given the plethora of armed forces involved in fighting in Iraq, including the Kurdish Peshmerga and the Popular Mobilisation Forces, a government-affiliated coalition of mostly Iranian-backed Shiite militias, there are major concerns on how the offensive will play out and whether it could unleash further sectarian violence.

McGurk said Washington was working to make sure that many security forces used in Mosul would be those trained by the coalition and that the roles of different forces would be agreed on ahead of the operation, which could begin as soon as October.

“We need to plan for the worst-case scenario, we can hope for the best but plan for the worst. We do not know what Daesh will do in Mosul,” he said.

Lise Grande, the UN humanitarian coordinator for Iraq, told the same meeting that Iraqi authorities had given reassurances that the screening of people leaving Mosul would be done by security forces and not by militias. Families would be transported either to an emergency camp or public buildings, she said.

Grande said Iraqi security forces would take steps to protect civilians, including alerting them of the upcoming campaign, identifying escape routes, and preparing safety cards.

The UN says the Mosul offensive risks triggering a major humanitarian crisis, with one million or more people potentially fleeing the city.

Stephen O’Brien, the UN aid chief, appealed to countries to speed up their aid donations ahead of the operation.

“To prepare for Mosul, partners launched a flash appeal for $284 million in July this year ... and 48 per cent of this funding, that’s $136 million, has been received,” he said.

“I cannot overstress the importance of receiving any outstanding pledges as soon as possible.”