Is the enemy of our enemy still our enemy?

Senior U.S. military leaders are uncertain whether the involvement of Iranian-based Shiite militias will turn out to be a help or a hindrance in the fight against the Islamic State (ISIS or ISIL) in northern Iraq.

“If they perform in a credible way” and free Tikrit from Islamic State control, “then it will, in the main, have been a positive thing in terms of the counter-ISIL campaign,” Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told members of the Senate Armed Services Committee last week.

Dempsey did not address Iran’s history of state-sponsored terrorism as a potential destabilizing factor in Iraq. His primary concern seemed to be the prospect of sectarian tension between the Shiite militia fighters and Tikrit’s mostly Sunni population.

“The important thing about this operation in Tikrit is less about how the military aspect of it goes, and more about what follows,” he told Agence France-Presse ahead of a visit to Bahrain and Iraq.

If Sunnis are allowed to return to their homes and “feel like the government is following an offensive with reconstruction and humanitarian assistance, then I think we’re in a really good place,” Dempsey said.

But if Sunnis are mistreated or forced out, and if the Baghdad government fails to deliver humanitarian aid, “then I think we’ve got a challenge in the campaign,” he said.

In the fight to retake the northern Iraqi city of Tikrit, Iraqi government troops make up only one-third of the force arrayed against the Islamic State. The remaining two-thirds of the estimated 23,000 troops is comprised of Iranian-based Shiite militia fighters, a great concern to many anti-ISIS coalition members, particularly Saudi Arabia.

According to The Telegraph, Prince Saud al-Faisal, the Saudi foreign minister, told U.S. Secretary of State John Kerry that by attacking ISIS positions only by air and refusing to send in ground troops, America is allowing the offensive in northern Iraq to be heavily influenced by Iran and its proxy Shiite militias, such as Hezbollah.

“Tikrit is a prime example of what we are worried about,” Prince Saud said. “Iran is taking over the country.”

He urged the U.S.-led coalition, of which Saudi Arabia is a member, to put “boots on the ground” against ISIS: “The kingdom stresses the need to provide the military means needed to face this challenge on the ground.”

But senior U.S. military officials are confident ISIS is on the defensive in Tikrit and that it is only a matter of time until it will be defeated without having to deploy large U.S. ground combat units. The group is not able to seize and hold new territory, as it did at the outset of its terror campaign, U.S. Army Gen. Lloyd Austin, commanding general of the U.S. Central Command, who oversees the military coalition fighting in Iraq, told the House Armed Services Committee.

Although Austin said U.S. and Iranian forces are not officially cooperating in the Tikrit operation, nevertheless the ground operation has been possible primarily because of the success of the U.S.-led air campaign, which puts senior U.S. officials such as Dempsey in the delicate position of welcoming the assistance of Iran in the tactical fight while remaining alert to the concerns of anti-ISIS coalition.

“I’m trying to get a sense for how our activities and their activities are complementary,” Dempsey told Agence France-Presse, referring to Iran’s support for the Shiite militias.

But a defeat of the Islamic State in Tikrit may come at the cost of spreading Iran’s destabilizing influence in the region, something Israeli Prime Minister Benjamin Netanyahu warned about in his March 3 address to a joint session of Congress.

“The struggle in Iraq between forces backed by Iran, not so covertly, and ISIS, is merely a struggle between two monsters vying for dominance,” noted columnist John Nantz. “As Netanyahu so eloquently put it, ‘When it comes to Iran and ISIS, the enemy of my enemy is my enemy.’”

The Associated Press contributed to this report.