Iraqi and Kurdish Peshmerga forces backed by U.S. air, artillery and forward air controller support began the battle for Mosul on Monday and gained ground in the drive for the city where the Islamic State declared the creation of a "Caliphate" more than two years ago.

"The thousands of ground combat forces who will liberate Mosul are all Iraqis," but they were supported by "a wide range of coalition capabilities, including air support, artillery, intelligence, advisers and forward air controllers," said Army Lt. Gen. Stephen Townsend, commander of Combined Joint Task Force-Operation Inherent Resolve.

The operation to retake Iraq's second-largest city, where as many as one million civilians remain under the control of the Islamic State of Iraq and Syria, "will likely continue for weeks, possibly longer," Townsend said in a video statement.

"There are Americans in harm's way as part of this fight. They're in a support role," Pentagon Press Secretary Peter Cook said, but some were moving forward with Iraqi and Kurdish forces amid reports that ISIS was using suicide car bombers to blunt the assault.

"It's fair to say there are Americans on the outskirts of the city," Cook said, but he was vague on how many U.S. troops are embedded with the advancing forces as advisers and Joint Terminal Attack Controllers to call in airstrikes.

"There was a plan for Americans to be providing that advisory role," he said.

Townsend has been given authority to embed U.S. advisers with friendly forces at the battalion level, but he has thus far "used that very sparingly," Cook said. "It's consistent with what we've done in the past," but "they are not in the lead in this fight. They are behind the forward line of troops."

U.S. AH-64 Apache helicopter gunships are also available for use in the Mosul fight, but Cook said that to his knowledge they had not yet been sent into action and it was unclear whether they would be.

In the retaking of Fallujah earlier this year, Iraqi Prime Minister Haider al-Abadi barred support from Apaches.

'A Hard Fight'

"Mosul will be a hard fight, but the Iraqi Security Forces are ready. They've been waiting to liberate Mosul for two years, and today is the day," said Army Maj. Gen. Gary Volesky, commander of Combined Joint Forces Land Component-Operation Inherent Resolve and commander of the 101st Airborne Division, in a statement.

The announcement that the campaign to retake the city had begun came from al-Abadi in a statement at 2 a.m. local time on state television.

"The Iraqi flag will be raised in the middle of Mosul, and in each village and corner very soon," said Abadi, who was dressed in a military uniform and surrounded by officers. Speaking to Mosul residents, he said, "We will liberate you from the terror and oppression of [the Islamic State]."

In Washington, Defense Secretary Ashton Carter said the start of the Mosul campaign was a "decisive moment" in the effort to defeat ISIS. "We are confident our Iraqi partners will prevail against our common enemy and free Mosul and the rest of Iraq from [the Islamic State's] hatred and brutality."

Without giving details on how much ground was gained in the first stages of the offensive, Cook said that "early indications are that Iraqi forces have met their objectives so far and that they are ahead of schedule for the first day."

Several villages east of Mosul reportedly were captured by Kurdish Peshmerga forces, while Iraqi Security Forces advanced from the south, according to the Iraqi Kurdish military command and a statement from Iraqi government forces.

ISIS fighters were "fleeing along southern axis of advance," ISF Maj. Gen. Hussein al-Awadi told the state-run Al Iraqiyah television channel, which was airing special "victory" music videos along with its news bulletins.

A statement by the General Command of Peshmerga Forces said that U.S. and coalition warplanes destroyed 17 ISIS positions ahead of advancing Kurdish troops, who also destroyed at least four ISIS Vehicle Borne Improvised Explosive Devices.

At the White House, Press Secretary Josh Earnest said the effort to take Mosul, if successful, would be a vindication of President Barack Obama's strategy in Iraq and Syria to keep U.S. troops out of ground combat and rely on local forces backed by U.S. airpower. "This would be the next step of this strategy."

'Victory Time'

Over the weekend, U.S. and coalition warplanes hit Mosul and surrounding areas in final "shaping operations" as officials said that preparations were complete for the offensive.

Iraqi aircraft dropped leaflets over the city declaring that it was "Victory Time" and warning residents to stay away from ISIS positions and seal their homes against what was expected to be a prolonged and difficult fight against an enemy that has had nearly two years to build defenses.

The leaflets included a phone number for residents to report the activity of ISIS militants to the uneasy alliance of forces that have converged to carry out the ground attack, restore central government rule and deal with an expected humanitarian crisis in the aftermath.

In northern Irbil, Kurdish Regional Government President Masoud Barzani said in a statement Saturday that "all preparations have been done to start the Mosul offensive and in this framework there is agreement between Peshmerga forces and the Iraqi army," the Kurdish Rudaw news agency reported.

On Sunday, U.S. Central Command reported that "attack, bomber, fighter, and remotely piloted aircraft conducted six strikes in Iraq, coordinated with and in support of the Iraqi government" over the weekend.

A strike in Mosul hit an ISIS weapons cache, CentCom said. And near the Qayyarah Airfield, the logistics hub for the Mosul offensive about 40 miles southeast of the city, airstrikes engaged an ISIS tactical unit, suppressed a rocket system and destroyed an ISIS building, a command and control node and an artillery system.

CentCom said that an ISIS remotely piloted aircraft also was destroyed but did not give details.

Time-Bomb Drone

Last week, Air Force Col. John Dorrian, a spokesman for Combined Joint Task Force-Operation Inherent Resolve, said that ISIS was deploying off-the-shelf drones, such as quad copters, and model airplanes as the attacking force moved closer to Mosul.

Dorrian said the drones were used mostly for surveillance, but a U.S. official, speaking on background, confirmed that one rigged as a time bomb had killed two Kurdish Peshmerga fighters.

In a briefing to the Pentagon last week from Baghdad, Dorrian said that the coalition had carried out 66 airstrikes against targets in Mosul over the previous two weeks. "The enemy is not going to be allowed to dig in at their leisure."

U.S. and Iraqi officials have said the fall of Mosul is inevitable, but Dorrian warned, "The size of Mosul makes this by far the largest task the ISF has undertaken to date, an order of magnitude larger than the liberation battles in cities like Ramadi, Fallujah and Sharqat."

Mosul was a city of two million -- Iraq's second largest -- before ISIS swept out of Syria in 2014 to take the city and large chunks of Iraqi territory against little resistance. About one million civilians are believed to remain in Mosul.

U.S. military and civilian officials have estimated that ISIS has about 3,000 to 5,000 fighters to defend the city. Residents of Mosul have reported to local media that ISIS has blocked likely avenues of attack with concrete barriers, dug an elaborate tunnel system and trenches, and planted numerous improvised explosive devices to blunt an attack.

The U.S. also fears that ISIS may resort to chemical weapons, possibly mustard gas, and has supplied the attacking force with protective suits and mask

A Fight to the Death

Recent reports from the region have suggested that the ISIS defenders are in disarray, with leaders fleeing the city and militants carrying out mass executions of defectors.

However, Kurdish forces approaching the city from the north and east have found signs indicating that ISIS is prepared to fight to the death.

Kurdish explosives ordnance personnel recently found a letter left behind for them in a village abandoned by ISIS, warning that more improvised explosive devices lie in wait in Mosul, according to Niqash, a non-profit media organization based in Berlin that has a network of Iraqi reporters.

"Your mission and my mission are never-ending," the letter said. "I lay the bombs and you dismantle them. Let's see which of us dies first."

"The speed at which they lay these IEDs is unbelievable," said Mohamed Ahmed, the head of the Iraqi Kurdistan Mine Action Agency. "There are some areas that were only under the IS group's control for a week. When they leave the area a week later, we find the place is absolutely full of IEDs."

To defeat the ISIS defenders, the Iraqi Security Forces have assembled 12 U.S.-trained brigades which, combined with Kurdish forces and Shiite Popular Mobilization Units linked to Iran, are expected to make up an attacking force of 20,000 to 30,000.

As happened in Fallujah and Ramadi, the main attack is expected to be led by the U.S.-trained Iraqi Counter-Terrorism Service units, the elite of the ISF.

A major concern for the U.S. is how the Iraqis will handle what is expected to be a massive flow of Mosul residents -- or Internally Displaced Persons -- fleeing the city now that the attack has begun.

In the retaking of Fallujah in Anbar province earlier this year, human rights groups and the United Nations charged that Shia Popular Mobilization Units allied with the Iraqi Security Forces committed atrocities in the "vetting" of refugees to weed out ISIS fighters.

With the addition of 600 U.S. troops last month, the U.S. now has more than 5,000 troops in Iraq, mostly acting as trainers and enablers for the Iraqis and the Kurdish forces.

In a State Department briefing earlier this month, Brett McGurk, the U.S. special envoy for Iraq and Syria, said there was a "humanitarian imperative" to take back Mosul quickly. He said the assault will be "a very unpredictable, very dynamic, very uncertain operation."

-- Richard Sisk can be reached at Richard.Sisk@Military.com.

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