President Barack Obama is right to focus on the responsibility of the Sunni Muslim world to attack and expunge the cancer that is the militant group calling itself the Islamic State (IS).

The group’s perversion of Islam in the service of its barbaric goals needs to be confronted first and foremost by those for whom it purports to speak.

But to succeed, the coalition must encompass the entire Muslim world and cannot exclude the most important Shiite nation, Iran.

Obama did not mention Iran in his brief comments Wednesday night, although he did make reference to “Sunni and Shia Muslims who are at grave risk, as well as tens of thousands of Christians and other religious minorities” that have been targeted by IS.

In a background briefing prior to the speech, a senior U.S. official repeated what has become an administration mantra that the U.S. does not “cooperate or coordinate military activity with Iran” when it comes to confronting IS.

However, deputy secretary of State Bill Burns has already raised the issue of Iraq with Iranian officials at least twice on the sidelines of negotiations over a long-term nuclear agreement. And Iran is due to participate in a meeting of foreign ministers in New York Sept. 19 during the UN General Assembly to discuss Iraq and the crisis created by IS.

Iran was instrumental in pushing aside Prime Minister Nouri al-Maliki in favor of Haider al-Abadi – the Iraqi Shiite the U.S. is counting on to form a more inclusive Iraqi government that Iraq’s Sunni minority can support. Iran is also fighting IS in Iraq through its assistance to the Iraqi government and the Kurdish Peshmerga. The U.S. and Iran both had advisers on the ground when these forces retook the Iraqi town of Amerli from IS – an effort augmented by U.S. air strikes. Some coordination between the U.S. and Iran certainly took place, even if it was only tacit.

The complication in extending the fight to Syria comes from the fact that Iran is also supporting the government of Bashar al-Assad. Assad, whose brutal oppression of the country’s Sunni majority helped revive IS, has lately begun to bomb IS positions after allowing the group to fester and spread for months in an apparent effort to discredit the entire Syrian opposition.

The stated U.S. goal now is to build up the so-called moderate Syrian opposition as an alternative to both Assad and IS. However, these moderates have been so disorganized and feckless in the past that they will certainly not evolve swiftly into a fighting force able to succeed against battle-hardened and well-equipped jihadis. To take back territory from IS, some elements of the Syrian regime’s forces will be needed.

As Matthew Olsen, director of the National Counterterrorism Center, told a Washington audience last week, “part of the broader strategy over the long term [against IS] is a political transition in Syria” that would remove Assad.

Assad is unlikely to be ousted without the acquiescence if not active involvement of Iran, which has become the Damascus’s regime most important regional partner.

No one is minimizing the challenge of forging a new Syrian regime that encompasses both regime elements and a substantial portion of the country’s Sunni majority. As in Iraq, it may be too late for such unity and a soft partition of the country into regions dominated by Assad, assorted Sunni groups and Kurds may be inevitable.

But the threat IS poses to the region should concentrate the minds of even historic sectarian and ethnic rivals. Sen. Carl Levin, in comments Thursday before the Council on Foreign Relations, said that IS “should be the glue that brings together the Muslim world.”

Levin, unfortunately, said he opposed including Iran in the anti-IS coalition. His argument was that this would somehow “muddy the waters” and interfere with efforts to conclude a long-term nuclear agreement with Iran.

While a nuclear deal is obviously the top U.S. priority with Iran at present, there is no reason to believe that it is not possible to work with Tehran on both issues. The U.S. and the other five permanent members of the UN Security Council plus Germany are not about to reduce their minimum requirements for a nuclear agreement just because of the IS threat any more than Iran would agree to give up enriching uranium for the sake of collaboration in Iraq and Syria.

In fact, openly including Iran in the anti-IS coalition might facilitate a nuclear deal by showing Iranians that the international community values its potential as a contributor to Middle East stability, not just to fighting militant, non-state groups.

As a country much more directly threated by IS than the United States, Iran has insights it can share and expertise it can bring to bear against this terrorist organization. Saudi Arabia appears to have recognized this by agreeing to a meeting with a senior Iranian official recently.

As President Obama said on Meet the Press last weekend, “the good news is … perhaps the first time, we have absolute clarity that the problem for Sunni states in the region, many of whom are our allies, is not simply Iran. It’s not simply a Sunni-Shia issue. Sunni extremism, as represented by ISIL [an alternative acronym for IS], is the biggest danger that they face right now.”

In 1991, the U.S. led a broad regional and international coalition against Saddam Hussein’s occupation of Kuwait that included Saudi Arabia. While Iran maintained neutrality in the conflict, the Iraqi air force was crippled by Tehran’s confiscation of aircraft that fled to Iran in the early days of the war. Two decades later, the U.S. can lead a similar coalition against an even more insidious foe.

Barbara Slavin is a senior fellow at the Atlantic Council’s South Asia Center and a correspondent for Al-Monitor.com, a website specializing in the Middle East. She is the author of a 2007 book, Bitter Friends, Bosom Enemies: Iran, the US and the Twisted Path to Confrontation, and is a regular commentator on U.S. foreign policy and Iran on NPR, PBS, C-SPAN and the Voice of America.

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