NORTHERN IRAQ – The Americans don’t trust the Iranians, the Iranians covet Iraq, the Sunnis and Shia have been at each other’s throats for 1,000 years and the Kurds prefer to be left alone.
As coalitions go, the one pieced together to dislodge ISIS from its Iraqi stronghold in Mosul is an odd one. For now, its members are working together, but uneasy alliances and divergent motives could be tested as fighting intensifies, experts told FoxNews.com.
"The Mosul offensive is being led by the government of Iraq and we, the coalition, are providing support by training police and military,” Pentagon spokesman and U.S. Marine Corps Maj. Adrian Rankine-Galloway told FoxNews.com, repeating the official line of all parties.
Coalition forces, including Iraqi Army soldiers, Kurdish Peshmerga fighters, Iranian ground troops, Shia militias and U.S. advisers, have freed outlying villages as they encircle the city ISIS captured more than two years ago. The black-clad jihadist army has ruled the city since it overran Iraqi Army soldiers in an assault that humiliated Baghdad and underscored the need for more training.
With the recent deployment of more than 600 troops, the U.S. has nearly 5,000 men and women on Iraqi soil and some 200 advisers deployed alongside Iraqi and Kurdish soldiers.
"Americans are in harm's way as part of this fight," Pentagon Press Secretary Peter Cook said last week. "They are playing a support role, but they are behind the forward line of troops."
Sources who spoke to FoxNews.com on condition of anonymity say they fear that, as the different teams converge on the city, any pretense of coordination could crumble.
"It is complete madness,” a U.S. military source within the high ranks of Operation Inherent Resolve told FoxNews.com. “It is Iraq we are supposed to be helping in this, but essentially, we are helping Iran."
Iran has never hid its desire to exert influence over its neighbor, even dating back to the 1980s, when it waged a grinding war with Sunni strongman Saddam Hussein’s Iraq. With a friendly government in Baghdad, Iran has sent troops into Iraq and legendary Revolutionary Guard Qassem Suleimani was spotted in the region earlier this week.
Galloway declined to comment on how strong Iranian influence is, saying "that would entail revealing classified information." But he insisted that no American forces would be commanded by Iran.
"U.S. troops answer to the commanding general Lt. Gen. Steve Townsend, commanding general of the combined joint task force international task force primarily manned by American forces," Galloway said.
But it is the Iranian-backed Shia militias who incite the most fear and hatred among coalition members. It was their fighters who used Tehran-supplied IEDs to kill more than 500 U.S. troops during the insurgency that followed the Iraq war. And they have used the cover of fighting ISIS to slaughter Sunni civilians in the liberation of other cities. Kurdish fighters told FoxNews.com they do not trust them, either.
The militias are playing a key role, particularly in clearing areas around Mosul ahead of the final push. With an estimated 6,000 mostly Sunni ISIS fighters holed up inside the traditionally Sunni city, Baghdad has barred Shia militias from entering the city out of concern they would commit atrocities.
"There is a reason we haven't been targeted by the Shia militias -- yet," said the U.S. source. "We are helping them get rid of their enemy, which is ISIS, but helping them gain a lot of power in the process."
Asked pointedly about cooperation with Iranian-backed Shiite militias, Rankine-Galloway said the U.S. "does not work with units that have histories of human rights abuses or officials with the government of Iran."
Shwan Mohommad Tihi, a former Iraqi Parliament member and head of the Security and Defense Committee in Baghdad between 2010 and 2014, called the mishmash of alliances "complicated."
"Iraq is Shia-dominated, so naturally Iran is going to have a lot of influence and Iran is not afraid to play here," Tihi said, indicating that a "bipolar" American policy and military presence has emboldened Iran. "Iran is gaining land and popularity because of this war in Iraq and the success of its proxies."
The Shia militias, known as Popular Mobilization Forces, are seen as an Iranian proxy. PMF Deputy Chief Moen Al Kadmi told FoxNews.com earlier this year they "don't want to work with U.S. troops" and insisted that U.S. forces had "fired on them."
"We won't kill them, but we can't guarantee that other militias won't kill them," he said ominously.
The PMF was formed in 2014 following a fatwa from Iraqi Grand Ayatollah Ali Sistani requesting able-bodied Iraqi men to expel ISIS, and while it has proven to be a strong fighting force, it is believed to include Iranian-controlled militias answering to Soleimani.
It’s not just the U.S. forces who have reason to distrust the Shia militias. One Kurdish Peshmerga lieutenant general stationed near the Syrian border said there is "no difference between Shia militias and ISIS."
"If we see militias here in our area, we will kill them," he said.
Shia militias not only "carry out mass atrocities" but they have another "dangerous agenda" in extending their influence across Iraq and Syria, a senior official with the Asayish, the main Kurdish security and intelligence branch, told FoxNews.com.
The agenda includes using the offensive as a pretext to place forces west of Mosul and extending to the Mediterranean Sea, an objective that prompted Turkey to send troops near Mosul. While Turkey is not officially part of the Mosul offensive, it is warily watching Iran, and could act if it sees a need to beat back its historic adversary.
“All parties here have an agenda here,” said the U.S. military source. “And it seems the U.S. [forces] are the only ones whose only priority is getting rid of ISIS."
Hollie McKay has been a FoxNews.com staff reporter since 2007. She has reported extensively from the Middle East on the rise and fall of terrorist groups such as ISIS in Iraq. Follow her on twitter at @holliesmckay