QAYYARAH, Iraq (AFP, REUTERS) - Iraqi forces were making gains as tens of thousands of fighters advanced on Mosul on Tuesday (Oct 18) in an unprecedented offensive to retake the city from the Islamic State in Iraq and Syria (ISIS) group.
With the crucial battle in its second day, Iraqi commanders said progress was being made as fighters pushed on two main fronts against the militants' last stronghold in Iraq.
The US military, which is leading a coalition providing air and ground support, said Iraqi forces even looked "ahead of schedule" but senior Western officials warned the battle would be long and difficult.
US President Barack Obama said on Tuesday that the push to liberate the northern city was a "major step forward."
"I am confident that ISIL will be defeated in Mosul and that will be another step towards their ultimate destruction," he told a joint news conference with Italian Prime Minister Matteo Renzi, using another acronym for the militant group.
But the US leader warned of a challenging road ahead. "Mosul will be a difficult fight. There will be advances and there will be setbacks," Obama said.
"Perhaps one million civilians are still living there," Obama added. "In addition to rooting out ISIL, our focus is on the safety and humanitarian aid for civilians escaping the fight. That will be a top priority for both our governments."
Advancing in armoured convoys across the dusty plains surrounding Mosul, forces moved into villages defended by pockets of ISIS fighters after intensive aerial bombardment.
At the main staging base for government troops in Qayyarah south of Mosul, federal police were rotating in and out of the front line.
As Apache attack helicopters flew overhead, ambulances brought the wounded back from the battle.
Two armoured vehicles bearing US flags drove by, apparently carrying American military personnel. One manning a gun turret flashed the victory sign.
Speaking to AFP from inside Mosul, resident Abu Saif said heavy smoke was hanging over the city as the militants burned tyres to shield themselves from air strikes.
While the sounds of explosions could be heard coming from outside the city, its streets were eerily quiet, the 47-year-old former company manager said.
"The streets are empty, the people have been staying at home since the strikes started yesterday," Abu Saif said.
"There is this happiness inside us... because we feel that we are about to be rescued," he said.
"But we are scared that Daesh (ISIS) can still carry out acts of revenge against the population."
The long-awaited Mosul offensive was launched on Monday, with some 30,000 federal forces leading Iraq's largest military operation since the 2011 pullout of US troops.
Retaking Mosul would deprive ISIS of the last major Iraqi city under its control, dealing a fatal blow to the "caliphate" the extremists declared two years ago after seizing large parts of Iraq and neighbouring Syria.
Iraqi commanders said ISIS fighters were hitting back with suicide car bomb attacks but that the offensive was going as planned.
"Many villages have already been liberated," said Sabah al-Numan, the spokesman of the elite counter-terrorism service.
"Iraqi forces have achieved their goals and even more, but we're careful to stick to the plan and not rush this."
The two main fronts are south of Mosul, where forces are moving from Qayyarah, and east, where another push involving Kurdish peshmerga fighters is under way.
In the south, forces inching forward along the Tigris river were training their sights on a village called Hammam al-Alil, while units east of Mosul entered Qaraqosh, once Iraq's biggest Christian town.
Iraqi forces have significant ground to cover before reaching the boundaries of the city, which ISIS is defending with berms, bombs and burning oil trenches.
ISIS forces are vastly outnumbered, with the US military estimating 3,000 to 4,500 militants in and around Mosul.
A video released on Tuesday by the ISIS-linked Amaq news agency showed masked fighters in battledress patrolling a deserted, dimly lit thoroughfare in what it said was Mosul.
"America will be defeated in Iraq and will leave, God willing, again - humiliated, wretched, dragging its tail in defeat," one of the fighters said to camera.
The US-led coalition said strikes destroyed 52 targets on the first day of the operation.
"Early indications are that Iraqi forces have met their objectives so far, and that they are ahead of schedule for this first day," Pentagon press secretary Peter Cook said.
Most of the coalition's support has come in the shape of air strikes and training, but US, British and French special forces are also on the ground to advise local troops.
"It could be a long battle, it's not a blitzkrieg... It's a lengthy affair (lasting) several weeks, maybe months," French Defence Minister Jean-Yves Le Drian told reporters in Paris.
France will host an international meeting Thursday on the political future of Mosul, while the coalition's defence ministers will meet in Paris next Tuesday (Oct 25) to assess progress on the military front.
Aid groups are bracing for a potentially massive humanitarian crisis, with some warning on Tuesday they were preparing for the possible use of chemical weapons by ISIS.
Mosul is Iraq's second-largest city and the UN fears that up to a million people could be forced from their homes by the fighting.
"There are real fears that the offensive to retake Mosul could produce a humanitarian catastrophe, resulting in one of the largest man-made displacement crises in recent years," warned William Spindler, spokesman for the UN refugee agency.
Both the Red Cross and the International Organisation for Migration raised concerns of ISIS using chemical weapons.
The Red Cross was training health-care workers and providing equipment to facilities around Mosul "that would be able to absorb the cases of people contaminated," Robert Mardini of the group's Near and Middle East division told reporters in Geneva.
Iraqi troops and police have been joined on the battlefront by an array of sometimes rival forces, including the Kurdish peshmerga, Sunni tribal fighters and Iran-backed Shiite militia.
ISIS once controlled more than a third of Iraq's territory but its self-proclaimed "state" has been shrinking steadily.
Experts warn that the militants are likely to increasingly turn to insurgent tactics as they lose ground.
The group has claimed a string of deadly suicide bombings in Baghdad in recent days.
ISIS has also organised or inspired a wave of attacks in Western cities and on Tuesday the European Union's security commissioner raised concerns over the potential impact of Mosul's fall.
"The retaking of the ISIS' northern Iraq stronghold, Mosul, may lead to the return to Europe of violent ISIS fighters," Julian King told German daily Die Welt.
He said even a handful of militants returning would pose a "serious threat that we must prepare ourselves for."