The United States and Iran have long been adversaries in Iraq, though both are Baghdad's allies. Now, as insurgents have swept across the north of the country, Washington and Tehran have reasons to work together. But could they? Here are five things to consider.
Who is talking about cooperation?
Both sides have said they are open to cooperating, without actually proposing it themselves. The overtures began when Iranian President Hassan Rohani said on June 14 Iran was ready to consider cooperating if Washington took action against Sunni extremist fighters in Iraq. On June 16, U.S. Secretary of State John Kerry said he "wouldn't rule out anything that would be constructive to providing real stability."
However, some red lines have appeared. The Pentagon has ruled out military cooperation with Iran. And Iran's National Security Council has ruled out military cooperation with Washington.
Initial contacts have reportedly taken place on the sidelines of the Iran nuclear crisis talks in Vienna, which began on June 16 and are due to end on June 20. But there has been no word on the outcome.
How strong is the motivation?
Analysts say the motivation to cooperate is strong because the Islamic State in Iraq and the Levant (ISIL/ISIS) poses threats not only to Iraq but far beyond.
The ISIL "poses a risk of conducting terrorist attacks not just in the immediate vicinity of Iraq but in the much wider region, including in the West," says John Drake, an Iraq specialist with risk-consulting firm AKE Group in London. "So the urgency of that situation means that they will have common ground to try to collaborate to counteract its spread."
ISIL is a Sunni fundamentalist organization that already has carved out a proto state across northern Syria, where it is fighting Tehran's ally Damascus. It is at war with Shi'ism, the official religion of Iran and, as an Al-Qaeda spin-off group, at war with the West. Its goal is to establish an Islamist caliphate in Iraq and the Levant based on its own extreme interpretation of Shari'a, or Muslim religious law.
What might cooperation look like?
Analysts say any cooperative strategy for rolling back ISIL in Iraq would likely be twofold: to neutralize the most extreme elements in the insurgent coalition while reaching out to those amenable to negotiations. The insurgent coalition includes hard-core jihadists, members of the reinvigorated Saddam-era Ba'athist Party, and multiple other Sunni militant groups, including some tribal leaders.
Part of the response to the threat, as Baghdad has already signaled, will be military. The Iraqi army, which was routed in fighting in Iraq's second city of Mosul and elsewhere, is now holding its own in the region around Baghdad. The army's effort is reinforced by Shi'ite militias.
"Shi'ite militias from Syria are coming back to Iraq, older militias are being reconstituted, and there is some evidence that [Iran's] Islamic Revolutionary Guards Corps (IRGC) itself is in Iraq, though in limited numbers," notes Fanar Haddad, an expert on Iraq at the Middle East Institute of the National University of Singapore.
The reported Iranian presence comes as Tehran has pledged to defend the Iraqi government. U.S. President Barack said on June 13 there could be U.S. military support but ruled out ground troops.
Analysts say the trick will be to turn the tide militarily against ISIL without the Shi'ite-led government's counteroffensive acquiring a sectarian appearance that further alienates Iraq's Sunni community.
Drake says that will require an outreach effort to moderate Sunnis that should involve Baghdad, Washington, and Tehran to assure them Iraq will become more inclusive of their community. The Kurds, another important power broker, will also need to be involved.
"The only thing that will really solve this is cooperation, dialogue, and negotiation," says Drake. "So the more people involved, the better it will be for all the different parties."
What stands in the way of cooperation?
Both Tehran and Washington would have to deal with domestic constituencies that strongly oppose cooperation with the other side.
"For both the American public and the Iranian public, cooperation with the United States or Iran is at best a tricky proposition for a domestic audience, and that is to say nothing of domestic politics and the political dynamics within the U.S. administration or the Iranian administration," notes Haddad.
In Washington, talk of cooperation with Iran drew immediate criticism from Obama critics such as Senator John McCain (Republican, Arizona), who called it "the height of folly." But another strong Obama critic and McCain ally, Senator Lindsey Graham (Republican, South Carolina), expressed support for cooperation.
Similar political complexity is likely in Tehran. Iranian President Hassan Rohan faces ultraconservatives who are already unhappy with his efforts to negotiate a solution with the West over Iran's nuclear crisis. But cooperation in Iraq could give Tehran a stronger bargaining position over its nuclear program, making the negotiations harder to criticize.
Equally uncertain is how the oil-rich Arab states, which regard Iran as a regional threat, might react.
"Prospective Iranian-U.S. cooperation intended to try to at least reduce the intensity of the civil conflict in Iraq would be resented by Saudi Arabia and the Gulf Arab states in particular," says Neil Partrick, associate fellow at the London-based Royal United Services Institute (RUSI).
"However it is not clear what alternatives these states have. They may like to see a challenge to the rule of the perceptibly pro-Iranian leadership embodied by [Iraqi Prime Minister Nuri] al-Maliki, but they also are as concerned about further Iraqi state disintegration and about so-called wash back from militant Sunni Arab, including Saudi, fighters there as they are in the case of Syria."
Because of such controversy, some analysts expect any U.S. and Iranian cooperation to take place quietly.
Haddad predicts that whatever happens, from the possible sharing of intelligence to the involvement of Iranian-funded Shi'ite militias, Washington and Iran will keep their role low-profile while trumpeting that of the Iraqi government.
"In terms of a concerted media campaign coming out of Baghdad, it will be the Iraqi forces that are spearheading the counterattack," says Haddad.
Today, it is too early to know whether any cooperation will take place. But it is interesting to note that Washington and Iran previously shared military intelligence to counter the Taliban in Afghanistan following the attacks on September 11, 2001.