Dubai: Iraqi government forces launched an offensive on Monday to drive Daesh from the northern city of Mosul, a high-stakes battle to retake the terrorists’ last major stronghold in the country.

Helicopters released flares and explosions could be heard on the city’s eastern front, where Kurdish fighters moved forward to take outlying villages.

A US-led air campaign has helped drive Daesh from much of the territory it held but 4,000 to 8,000 fighters are thought to remain in Mosul.

Residents contacted by phone dismissed reports of an exodus by the terrorists, who have a history of using human shields and have threatened to unleash chemical weapons.

“Daesh are using motorcycles for their patrols to evade air detection, with pillion passengers using binoculars to check out buildings and streets,” said Abu Maher.

He and others contacted were preparing makeshift defences and had been stockpiling food in anticipation of the assault, which officials say could take weeks or even months.

The United States predicted Daesh would suffer “a lasting defeat” as Iraqi forces mounted their biggest operation in Iraq since the 2003 invasion that toppled Saddam Hussain.

Turkish President Recep Tayyip Erdogan on Monday said Turkey would play a role in the offensive, saying it was unthinkable for Ankara to stay on the sidelines.

“We will be in the operation and we will be at the table,” Erdogan said in a televised speech. “Our brothers are there and our relatives are there. It is out of the question that we are not involved.”

The build-up for the offensive was marked by a bitter squabble between Ankara and Baghdad over the planning.

Turkey had raised concerns over the possible involvement of Iraqi Shiite and anti-Ankara Kurdish militia in the offensive, while Baghdad had lashed out at the presence of a contingent of Turkish troops in Bashiqa, north of Mosul.

In a sign Ankara was trying to lower the temperature with Baghdad, Deputy Prime Minister Numan Kurtulmus said that a top-level Turkish delegation led by foreign ministry undersecretary Umit Yalcin was on its way to the Iraqi capital for talks.

The United Nations’ humanitarian coordinator for Iraq said the military had told the UN it expected the first significant population movement to begin in five to six days, suggesting that is when the assault would move to the city itself.

Lise Grande said Iraqi security forces would transport fleeing civilians, who would be vetted to ensure Daesh fighters could not hide among them, following residents’ reports that militants had shaved off their beards to escape detection.

The commander of the coalition, US Lieutenant General Stephen Townsend, said the operation to take Iraq’s second largest city would likely continue for weeks, “possibly longer”.

If Mosul falls, Raqqa in Syria will be Daesh’s last city stronghold.

The United Nations has said the battle would require the world’s biggest and most complex humanitarian effort, which could leave up to 1 million people homeless and see civilians used as human shields or even gassed.

- with inputs from agencies