AL-SHURA -  Iraqi forces launched an offensive Monday to retake Mosul and deal a death blow to the Islamic State group’s “caliphate” in the city where it was declared two years ago.

The start of the long-awaited assault raised deep concerns for hundreds of thousands of civilians trapped in Iraq’s second-largest city, with aid groups warning of a massive humanitarian crisis.

Some 30,000 federal forces are leading the offensive, backed by air and ground support from a 60-nation US-led coalition, in what is expected to be a long and difficult assault on IS’s last major Iraqi stronghold.

Iraqi forces could be seen readying weapons and ammunitions as columns of armoured vehicles headed towards Mosul from the town of Al-Shura, some 45 kilometres (30 miles) south of the city.

The Pentagon described the operation as a “decisive moment” in the fight against IS but the US-led coalition’s top commander warned it could last weeks or more.

Iraqi Prime Minister Haider al-Abadi announced the beginning of the assault in a televised address in the early hours of Monday.

“Today I declare the start of these victorious operations to free you from the violence and terrorism of Daesh (IS),” Abadi said.

IS seized control of large parts of Iraq and neighbouring Syria in mid-2014, declaring a cross-border “caliphate” and committing widespread atrocities.

The militants have suffered a string of territorial defeats this year in both countries, and the retaking of Mosul would all but end the group’s presence in Iraq as a land-holding force. Iraqi forces have been closing in on Mosul in recent weeks but the battle launched on Monday could be the toughest yet in the fight against IS.

IS forces are vastly outnumbered, with the US military estimating that 3,000 to 4,500 militants are in the city and surrounding area. But they have had months to prepare and will seek to use hit-and-run tactics, ambushes, snipers, bombs, berms and trenches to slow down and bleed Iraqi forces.

As the assault began, federal forces moved from their main staging base of Qayyarah, south of Mosul, while peshmerga forces from the autonomous Kurdish region advanced from the east.

Around 4,000 Kurdish peshmerga took part in a push to reclaim villages once inhabited by members of the Christian and Kakai minorities, a statement said.

At a staging area near the village of Khazir east of Mosul, Kurdish forces could be seen firing artillery and rockets as smoke rose from houses in the distance.

Abadi stressed that only Iraqi police and army would enter the city.

“The force leading liberation operations is the brave Iraqi army with the national police and they are the ones that will enter Mosul, not others,” he said.

The United Nations and other aid organisations warned that a huge number of civilians were in immediate danger. “I am extremely concerned for the safety of up to 1.5 million people,” the UN deputy secretary general for humanitarian affairs and emergency relief, Stephen O’Brien, said.

“Depending on the intensity and scope of the fighting, as many as one million people may be forced to flee their homes in a worst-case scenario,” O’Brien said in a statement.

The Norwegian Refugee Council said safe exits from Mosul must be provided or civilians “will be faced with the bleakest of choices: stay behind and risk their lives under attack, or risk their lives trying to flee.”

Iraqi forces advancing on multiple fronts are some distance from Mosul and are expected to eventually take up positions on the edge of the city and lay siege before breaching its boundaries and directly engaging die-hard militants.

“This operation to regain control of Iraq’s second-largest city will likely continue for weeks, possibly longer,” warned Lieutenant General Stephen Townsend, commander of the US-led coalition.

Most of the coalition’s support has come in the shape of air strikes and training but US, French and British special forces are also on the ground to advise local forces in battle.

“This is a decisive moment in the campaign to deliver ISIL a lasting defeat,” US Secretary of Defence Ash Carter said, using an alternative acronym for the militant group.

 

President Recep Tayyip Erdogan on Monday indicated that Turkey would also play a role in the offensive despite concerns raised by Baghdad over Ankara’s involvement.

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

IS once controlled more than a third of Iraq’s territory but its self-proclaimed “state” has been shrinking steadily. It lost its emblematic bastion Fallujah in June, the Anbar provincial capital Ramadi months earlier and on Sunday Syrian rebels retook the town of Dabiq, which held special ideological significance for the group.

If Mosul falls to Iraqi forces, only Raqa in Syria would remain as the last major city in either country under IS control.

But even the recapture of Mosul will not mark the end of the war against IS, which is likely to increasingly turn to insurgent tactics as it loses more ground.

 

Just hours after the offensive was launched, IS claimed responsibility for a suicide car bombing targeting an Iraqi army checkpoint south of Baghdad that killed at least 10 people.

The militants have claimed a string of deadly bomb attacks in Baghdad in recent days.

The militants’ defeat in Mosul appears to be only a matter of time and some military sources suggest an exit route for fleeing militants could be left open in a bid to minimise the fighting and its potential impact on the city’s population and infrastructure.