JUDY WOODRUFF: Longstanding rivalries were re-ignited in Iraq today between vital American allies.

Iraqi military forces and militia moved to push Kurdish forces out of the disputed city of Kirkuk in the country’s north.

Lisa Desjardins begins our coverage.

MAN (through interpreter): The commander in chief of the armed forces, Dr. Haider al-Abadi, gave orders to protect the people of Kirkuk and to impose security in the city.

LISA DESJARDINS: After months of simmering tensions, Iraqi federal troops moved to retake the disputed city of Kirkuk from Kurdish forces.

The effort launched before dawn. By midday, Iraqi soldiers, along with state-backed militias, quickly took control of several massive oil fields north of the city. Iraqis also captured Kirkuk’s military airport and various government buildings. They lowered what had been a symbolic Kurdish flag at the governor’s compound.

Journalist Rebecca Collard in Irbil was in Kirkuk this morning.

REBECCA COLLARD, Journalist: You could hear some clashes, some gunfire in the distance, but for the most part, the city seemed more or less abandoned. Now, the Iraqi army, by the end of today, was essentially in control of the whole city and many of the outskirts of Kirkuk.

LISA DESJARDINS: The spokesman for an Iraqi Shiite militia said they achieved all their goals with little resistance.

AHMED AL-ASSADI,  Spokesman for al-Hashed al-Shaabi (through translator): As the troops approached the area, they were confronted by some rebels, who tried to hinder the progress of the advancing units. Our troops returned fire and silenced its source.

LISA DESJARDINS: This comes three weeks after the Kurds held a nonbinding independence referendum that included the disputed province of Kirkuk.

More than 90 percent of the Kurdish region’s residents voted to split from Iraq. The Iraqi federal government, Turkey, Iran and the U.S. all rejected the independence drive.

The multiethnic region of Kirkuk lies just outside of the autonomous Kurdish region in Iraq’s north. Called the country’s oil capital, Kirkuk produces around 500,000 barrels a day.

In 2014, amid the ISIS onslaught across Northern Iraq, the Kurds took control of Kirkuk, as the Iraqi military fled the city. In the three years since, the Kurds, led by their president, Massoud Barzani, sought to cement their hold, despite tensions with the central government.

Today, Kurdish officials accused Iraq of carrying out a major multipronged attack.

MAJ. GEN. AYOUB YUSUF SAID, Peshmerga Commander (through interpreter): I don’t know what is happening exactly, because we have been in this fight since 4:00 in the morning. We have suffered casualties, including martyrs, and now we have withdrawn to this position. Some of the other Kurdish forces have pulled out. They didn’t fire a single shot.

LISA DESJARDINS: While Kurdish forces withdrew from posts south of the city, some residents vowed to die fighting. Thousands of others fled north.

REBECCA COLLARD: For the last few years, the Iraqi forces, these primarily Shia militia, the Hashed Shaabi, and the Kurdish forces have been focused on fighting ISIS. Now that fight is coming to an end, and what the fear is that now these internal division in Iraq are going to become more apparent and possibly more violent.

LISA DESJARDINS: These clashes pit one substantially American-armed military force against another. Both the Kurdish forces and Iraqi government troops are part of the coalition fighting ISIS. The U.S. sought to downplay the fighting, labeling the exchange of gunfire a misunderstanding.

And, in the Rose Garden, President Trump tried to stay neutral.

PRESIDENT DONALD TRUMP: We don’t like the fact that they’re clashing. We’re not taking sides. But we don’t like the fact that they’re clashing.

LISA DESJARDINS: For the PBS NewsHour, I’m Lisa Desjardins.

JUDY WOODRUFF: For more, I’m joined now by Emma Sky. She served as an adviser to General David Petraeus while he was commander of U.S. forces in Iraq from 2007 to 2010, and by Feisal Istrabadi. He’s a former Iraqi ambassador to the United Nations and he helped write Iraq’s interim constitution.

Welcome to both of you.

Let me start with you, Emma Sky.

This has happened so quickly. What exactly has the Iraqi government done?

EMMA SKY, Yale University: The Iraqi government has deployed its forces back up north into Kirkuk.

And since 2003, the Kurds have made it clear that they want to include Kirkuk within their territory in order to proceed with gaining independence, which has always been their goal. But Kirkuk is important to Iraq itself, and no Iraqi prime minister can afford to lose Kirkuk.

So you can see this reaction that has taken place following the referendum on independence, which happened September the 25th, and also included the disputed territories and the city of Kirkuk.

JUDY WOODRUFF: Feisal Istrabadi, what can you add to why the Iraqi government is so set on taking over the city?

FEISAL ISTRABADI, Former Deputy UN Ambassador, Iraq: Well, a couple of reasons.

First, as Emma just said, it is a part of the disputed territories, which are legally and constitutionally under the jurisdiction of the federal government in Baghdad. The KRG expanded into these disputed territories at the time when ISIL was expanding its territory, and then began to take steps to unilaterally declare that these areas were now incorporated into the Kurdistan region, including when it held the referendum that Emma talked about.

It included holding the referendum in these disputed territories. Now, so long as Iraq — so long as we’re talking about a single country, it matters a little less who controls Kirkuk, but once the referendum was held, this gave rise then to the second reason for Baghdad choosing to act now.

As Emma said, Kirkuk is an important oil-producing zone in Iraq. And it is vital for the economic viability of an independent Kurdish state and an important part of the economic viability of the Iraqi state. So there was never going to be a scenario, I think, in which Baghdad would allow a unilateral exercise of control by Kurds to occur over Kirkuk, so long as independence is on the table.

JUDY WOODRUFF: Emma Sky, we heard President Trump say today the U.S. is not taking sides in this.

Is that accurate, that the U.S. isn’t taking sides? What is the U.S. role here?

EMMA SKY: Well, the U.S. has stipulated over and over again that its policy is to support a united Iraq.

So you can see the U.S. has given support to Iraqi security forces, but also to the Kurdish Peshmerga, to fight against ISIS. The U.S. policy for the last few years has really been focused on ISIS and not on the day after ISIS.

But what we’re witnessing at the moment is that different groups are already moving to the day after, which is the power struggle for control of different territories in Iraq.

And Barzani believed that during the fight against ISIS, he became stronger because he got weapons directly from the international community. And, as Feisal said, he was able to extend his control over the disputed territories.

He’s also facing domestic problems within Kurdistan. There are tensions between the different Kurdish groups, and some believe that Barzani has overstayed his term as president.

JUDY WOODRUFF: Which reminds us just how complicated this is, Feisal Istrabadi.

What does the Iraqi central government want here? They’re not going to get rid of the Kurds. What is it that they want?

FEISAL ISTRABADI: Oh, well, I mean, the Kurds of course are a vital part of Iraq. They’re a vital part of the political process, and they have been represented in Baghdad. The president of Iraq is a Kurd and has been since 2005.

I think what needs to occur and I hope what the government of Iraq wants is a negotiated settlement, in which no party dictates terms to the other, but a negotiated settlement.

Look, Irbil has some legitimate agreements with respect to Baghdad. Baghdad has some legitimate agreements with respect to Irbil. I think we need a mediator perhaps or somebody to convene a roundtable — the United States is who I’m thinking of, of course — to address some of those issues.

Most of the issues are, from the Irbil side, economic issues of payments, and from Baghdad’s side, transparency of how much oil Irbil is producing and exporting, which Irbil has never accounted for to Baghdad.

I think if those issues are resolved, perhaps hopefully some of these other issues can at least be delayed for another day. But at the end of the day, neither government — neither the regional government nor the federal government in Baghdad can really tolerate dictation of terms to it by the other side. My hope is that a negotiated settlement obtains.

JUDY WOODRUFF: Emma Sky, where do you see this going from here? Do you see the peace that different sides have worked to hard to create in Iraq unraveling as a result of this?

EMMA SKY: I think there is an opportunity for a deal, and I think the sort of deal that could be negotiated is one that looks at a special status for the city of Kirkuk and negotiated terms for Kurdistan’s separate, whether that be towards confederation or towards independence.

But there needs to be negotiation. There needs to be a look at where should the border between Iraqi Kurdistan and the rest of Iraq actually be, and that requires mediation district by district through those territories.

JUDY WOODRUFF: Well, we know there are other players who are playing an important role here in Iran and Turkey, and this is all very much playing out as we watch, watch it happen in Iraq.

Emma Sky, Feisal Istrabadi, thank you very much.

FEISAL ISTRABADI: Thank you.

EMMA SKY: Thank you.

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