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Twice designated a terrorist by the United States government, considered responsible for up to 20 percent of American casualties in the Iraq war, Major General Qasem Suleimani, the legendary Iranian spymaster and leader of the Quds Force – the elite special operations wing of the hardline Revolutionary Guard Corps (IRGC) – is now stirring alarm in Washington for doing something the Obama administration would ordinarily cheer: taking the fight to ISIS in Iraq.

Photographs circulating on social media show Suleimani operating alongside senior Iraqi officials in the theater in and around Tikrit, the Sunni ancestral home of Saddam Hussein that is located almost equidistant between Mosul, the ISIS-controlled city 120 miles to the north, and Baghdad, the capital of the Iraqi government 100 miles to the south.

The presence of Suleimani at the forefront of Iraqi forces’efforts to reclaim Tikrit from ISIS control underscores both the expanding influence of Iran on the central Iraqi government and the increasingly critical role that Shi’ite militiamen, thought to be operating under Quds command, are playing in the Iraqi fight against ISIS. Neither development brings pleasure to senior U.S. officials or lawmakers in Congress.

Rep. Rodney Frelinghuysen, R-N.J., raised the issue of the Iranians with President Obama’s new defense secretary during a House Appropriations defense subcommittee hearing on Wednesday. “I know we're keeping our distance physically from them in Baghdad,” Frelinghuysen said. “Have we ceded most of the governance of Iraq to Iranians?...And will the military operations that are undergoing, which we are watching, divide the country and require us in some ways to spend more of our resources?”

“I absolutely share your concern about the role of Iran in Iraq and the wider region,” Defense Secretary Ashton Carter told the panel.

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    Among those concerns is a fear about what may happen if and when ISIS fighters surrender or flee Tikrit, which is presently said to be encircled and witnessing combat. Of the advancing forces, two-thirds are believed to be Shi’ite militiamen loyal to Iran, with the remainder belonging to Iraqi security forces, and officials worry that the Shi’ite troops may seek to avenge ISIS’ massacre of 1,700 Iraqi troops, almost all Shi’ites from nearby Camp Speicher, last June.

    “The killings that were perpetrated in the time after we left Iraq would never be forgotten,” Frelinghuysen said.

    “I completely agree with you,” Carter replied. “And sectarianism is one of the things that concerns me very much. And of course, it's the root of the Iranian presence in Iraq.”

    “We're watching carefully,” added U.S. Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, who appeared alongside Carter at the hearing. “If this becomes an excuse to ethnic cleanse, then our campaign has a problem and we're going to have to make a campaign adjustment.”

    An additional reason the battle for Tikrit bears close watching at the Pentagon is because it may serve as an indicator of how well the Iraqi forces and their Shi’ite comrades can perform when the larger contest for Mosul is engaged. Analysts who have examined recent Iranian casualty reports said the data show the Islamic regime deploying more rank-and-file troops to Syria, but higher-level commanders to Iraq, to oversee the Shi’ite militia groups.

    Ali Alfoneh, an Iranian-born scholar at the Foundation for the Defense of Democracies, cast the involvement of the Quds Force in the ISIS conflict as reflecting a larger trend in Iranian society: its slow transformation from a radical Islamic theocracy to a military dictatorship, with the IRGC assuming ever greater powers.

    “This is an organization which has engaged in spreading sectarian terror in Iraq. And now, this is the force that the Iraqi government has turned to for help in order to liberate Tikrit from Islamic State terrorists,” Alfoneh told Fox News. “In other words, we have one terrorist organization which is helping the Iraqi government get rid of another terrorist organization.”

    Such tangled lines of authority and influence are exactly what Israeli Prime Minister Benjamin Netanyahu had in mind on Tuesday, when he told a joint meeting of Congress: “When it comes to Iran and ISIS, the enemy of your enemy is your enemy.”