A helicopter belonging to the international coalition forces takes off from a base outside Mosul, Iraq, Wednesday, Oct. 19, 2016. The U.S. has just as much to gain from the operation to recapture Mosul as the Iraqis themselves. Since 2014, the U.S. has provided airstrikes and advise-and-assist operations to put the beleaguered Iraqi military back on its feet after the Islamic State group gutted it of weapons, supplies and soldiers during its blitzkrieg across Iraq and Syria. (AP Photo)

WASHINGTON - As Iraqi tanks charge across the country to purge the city of Mosul of the Islamic State group, the United States has perhaps as much to gain from the operation as the Iraqis themselves. Wresting Iraq's second largest city from the extremists is key to eventually defeating them militarily, a major U.S. objective. Still, President Barack Obama's strategy to engage in this war without the use of combat forces has been received with some skepticism; some say this approach allowed IS to expand in the first place.

Since 2014, the U.S. has provided advise-and-assist operations to put the beleaguered Iraqi military back on its feet after IS gutted it of weapons, supplies and soldiers during its blitzkrieg across Iraq and Syria. A U.S.-led coalition later launched airstrikes in Iraq and Syria, reinforcing Iraqi, Kurdish and Syrian ground forces, while maintaining that no foreign combat troops would take part in the fight.

A look at the U.S. role against IS:

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HOW MANY U.S. SOLDIERS ARE CURRENTLY IN IRAQ AND SYRIA?

According to the Pentagon, there are 4,815 U.S. troops in Iraq, including special operations forces. The Obama administration has authorized a maximum troop level of 5,262. That number does not include as many as 1,500 troops on temporary duty or short-term contracts.

In Syria, the Obama administration has authorized 300 troops — most of them special operations forces who mainly work with the Syrian Democratic Forces, a coalition of Kurdish and Arab allies. Medical and logistics units are also included in that number.

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WHERE ARE THEY LOCATED?

U.S. forces in Iraq use bases in the cities of Baghdad, Irbil, Taji and Habaniyah. There are also "several hundred" American troops at the military base in Qayara West, south of Mosul, where they are helping build a staging area for the Iraqi security forces operation to recapture the city, according to a U.S. military official, who spoke on condition of anonymity because the details haven't been made public.

In northern Syria, details are not released, given the sensitivity of the operations. U.S. support is ultimately aimed at helping the Syrian Democratic Forces advance on Raqqa, Islamic State's de facto capital. U.S. special operations forces sometimes stay in the country for several weeks at a time.

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WHAT IS THE OVERALL MISSION?

In Iraq, U.S. advisers, trainers, special operations forces and others are stationed at Iraqi bases, working with Iraqi forces. Some U.S. advisers work at the division headquarters level. Others are deployed at the brigade and battalion level, meaning they are embedded with smaller units, closer to the fight.

A U.S. official said there are now more than 100 special operations forces embedded with Iraqi special operations forces and Kurdish Peshmerga fighters.

The official, who spoke on condition of anonymity since the matter has not been made public, said there are small teams of about a dozen troops each, including force protection, communications, medical, engineering and forward air controllers, who help call in airstrikes. These teams are embedded at the battalion or headquarters level and they will continue to move with those units, but will stay behind the forward line of troops, the official said.

American forces dealing with Syria are based in neighbouring countries, such as Turkey and Iraq, and travel in and out of Syria, at times staying there a few days at a time. They provide advice and other assistance, but do not fight alongside the Syrians. Pentagon officials say that U.S. Special Forces have carried out about 400 missions in Syria to date.

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HOW IS THE AIR CAMPAIGN GOING?

Since airstrikes began in August 2014, over 10,200 airstrikes had been carried out in Iraq and nearly 5,600 in Syria. August saw a second consecutive month that coalition airstrikes in Syria outnumbered those in Iraq.

According to Chris Woods, director of the Airwars project, a group that tracks and archives data from the international air war against IS, only 7 per cent of the airstrikes being conducted in Iraq and Syria were by Reaper and Predator drones.

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WHO ARE PARTNERS OF THE U.S.?

The vast majority of airstrikes in both Iraq and Syria are conducted by the U.S. Coalition partners include the United Kingdom, Canada, France, Denmark, Australia, Saudi Arabia, Jordan, the United Arab Emirates, the Netherlands, Belgium and Bahrain.

Backed by coalition airstrikes, Turkey has also sent tanks, warplanes and special operations forces into northern Syria. Turkey's objective has been twofold: It's looking to clear IS militants from its remaining border stronghold, while also rolling back any advances made by Syrian Kurdish militias, which Turkey regards as a significant national security threat.

Russia backs Syrian President Bashar Assad. Russia's air force, along with that of Syria, has been bombing targets in the country, including those of IS. Russia is not part of the U.S.-led coalition, but Russia and the U.S. have worked out limited co-ordination on flights to maintain airspace safety and avoid collisions.

But diplomatic talks with Russia disintegrated this month after the U.S. formally accused Russia of trying to meddle in the U.S. election by hacking U.S. political groups. Secretary of State John Kerry also accused the Kremlin of war crimes in Syria, all but ending efforts to boost co-operation between Washington and Moscow on the issue of Syria.

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SO, WHERE DO WE STAND ON THE MOSUL OPERATION?

Timeframes provided by American and Iraqi officials for recapturing Mosul is generally a few weeks, or longer.

East of Mosul, about 2,000 Kurdish Peshmerga fighters, backed by coalition air- and artillery strikes, are conducting an operation dubbed Evergreen II, designed to seize and control key terrain near the Gaur River Bridge and the Great Zab River.

Coalition-supported forces have also cleared five villages around Mosul, including Qayara, which will be used as a critical staging ground for the Mosul operation, as well as a centre for humanitarian efforts.

The coalition is providing training to remove many of the explosive remnants of war that IS fighters typically leave behind once they've been driven from an area. It is also conducting multiple strikes around the city with the goal of denying the militants access to critical infrastructure and resources, including the Tigris River.

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Associated Press writer Lolita Baldor contributed to this report from Washington.

News from © The Associated Press, 2016