BAGHDAD: U.S. air support and pledges of weapons and training for Iraq’s army have raised expectations of a counteroffensive soon against ISIS, but sectarian rifts will hamper efforts to forge a military strategy and may delay a full-scale assault.

The ultra-extremist group spearheaded through northern Iraq in a 48-hour offensive in June, charging virtually unopposed toward the outskirts of Baghdad, humiliating a U.S.-trained Iraqi army which surrendered both land and weapons in its retreat.

By contrast, even a successful effort by the Shiite-led government to dislodge ISIS from Sunni territory where it rules over millions of Iraqis would be fiercely fought and could stretch well beyond next year.

The Baghdad government relies on Shiite militias and Kurdish peshmerga to contain ISIS – a dependence that underlines and may even exacerbate the sectarian rivalry which opened the door for the summer offensive.

U.S. newspapers have cited officials in Washington as saying the Americans’ training mission aims to prepare Iraqi troops for a spring offensive to retake territory, including Mosul, northern Iraq’s largest city and ISIS’ powerbase.

Hemin Hawrami, an official close to Kurdish leader Massoud Barzani, told Reuters that Iraqi forces would not be ready to take the fight to Mosul, in Iraq, until late 2015.

“There will be no spring or summer [offensive],” he said, adding that progress depended on government willingness “to reorganize the army, how quickly they can solve political issues with us and the Sunnis, [and] how quick the coalition will be in providing heavy arms to peshmerga and the Iraqi army.”

The army, Shiite militias and Kurdish fighters have made some gains against ISIS, pushing back an advance toward Kurdish territory in August and last week recapturing towns in Diyala province, on the road from Baghdad to Iran.

The leader of the pro-Iranian Shiite Badr Organization, whose fighters battled alongside peshmerga and soldiers in Diyala, said they would turn next to the Sunni provinces of Salahuddin and Anbar – north and west of Baghdad – before moving further north to Nineveh province, where Mosul lies.

“We are counting on the support of the Sunni tribal fighters. With them joining the fight, our victory is certain,” Hadi al-Amiri told Reuters by telephone from Diyala province.

Amiri said he expected to get weapons not just from the Iraqi government, which may allocate a quarter of next year’s $100 billion budget to the military, but also from the $1.6 billion of arms and training, which Washington plans to deliver.

Both Amiri’s assumptions look optimistic, as Washington and the Sunni tribes are deeply wary of Shiite militia forces.

Iraqi authorities aim to overcome the deep rifts between Shiites, Sunni Arabs, Kurds and other groups by absorbing local fighters into a state-funded National Guard, but the role of that force remains undecided.

Government adviser Zuhair al-Chalabi told Reuters the army was in no shape to surge north and Mosul’s mainly Sunni residents would resist a campaign by Shiite militias alone.

Instead, a combined force of army soldiers, Sunni tribes, Kurdish peshmerga and Shiite fighters must be assembled – and the open border with ISIS territory in Syria sealed.

“There is a plan, but it can’t be implemented that quickly,” said Chalabi, who is from Mosul.

Finance Minister Hoshyar Zebari said ISIS was still a formidable force but was losing the ability to conduct major ground combat because that exposed it to airstrikes.

Zebari, a Kurd, declined to give details of the military strategies of either the Baghdad government or the semi-autonomous Kurdish authorities, but said “planning and coordination are already underway” for the battle for Mosul. “I am really not aware of spring offensives. The offensive is on – spring, summer, winter. We countered them in autumn. This is an ongoing battle with them.”

The United States is setting up four training camps for Iraq’s 80,000-strong armed forces – two around Baghdad, one in the Kurdish city of Irbil and the fourth in Anbar.

Washington has also set out plans to provide body armor and guns to 45,000 troops, 15,000 Kurdish peshmerga and 5,000 Sunni tribal forces.

A senior Western diplomat in Baghdad said the training might take six months, with the first round complete in late spring.

While he argued that the tide had turned against ISIS in northern Iraq and was moving against it elsewhere, fighting was likely to stretch into 2016.

And without control over the border, ISIS fighters could slip away and regroup in Syria. “It’s the balloon theory. You squeeze one part and it pops up elsewhere,” he said.

Hawrami, the Kurdish official, foresaw a protracted and potentially inconclusive battle.

“To guarantee their defeat in Mosul we have to defeat them in Syria as well,” he said. “ISIS cannot be vanquished. ISIS can be degraded and weakened, but this process of degrading and weakening needs years.”