BAGHDAD >> Kurdish separatists in northern Iraq surrendered all disputed oil fields to Iraq’s military today, retreating in the face of overwhelming force that appeared to halt, at least for now, their independence hopes from a referendum held less than a month ago.

In a swift and largely nonviolent operation that came a day after Iraqi forces reclaimed the contested city of Kirkuk from the Kurdish separatists, Baghdad’s troops occupied all oil-producing facilities that the separatists had held for three years, and which had become critical to the Kurdish autonomous region’s economic vitality.

The loss of those resources will erase billions of dollars in export earnings that has flowed to the Kurdish region from the sale of oil. Kurds took over the disputed areas adjacent to their region after Iraqi troops fled an assault by the Islamic State extremist organization in 2014.

Those areas were included in the Sept. 25 referendum in which the Kurdish region voted overwhelmingly for independence. The vote angered not only the central government in Baghdad and the United States, but also neighbors Turkey and Iran, which have sizable Kurdish populations.

The Iraqi military operation to retake the disputed areas was aided by an agreement with a Kurdish faction to withdraw from them peacefully.

The territorial surrender, and its economic importance, raised new doubts about the political future of the Kurdish president, Massoud Barzani, the driving force behind the referendum, who was clearly outmaneuvered by the Iraqi prime minister, Haider al-Abadi.

At a news conference in Baghdad today, al-Abadi said the referendum “is finished and has become a thing of the past.”

Barzani and other supporters of the referendum “took a very bad situation and made it worse,” said Denise Natali, a Middle East specialist at the National Defense University in Baghdad.

“Barzani badly miscalculated,” she said. “He played it all wrong.”

In his first public statement since Iraqi forces launched the takeover operation on Oct. 16, Barzani blamed members of the rival Kurdish faction for having withdrawn from contested areas and said that had “unilaterally paved the way for the attack.”

Barzani seemed to warn Baghdad not to advance beyond those areas.

“All resources will be allocated for the security and stability of the Kurdistan region,” the statement said.

Nonetheless, it was unclear how much support Barzani had to back up his bluster. He is isolated in the Kurdish region, where Baghdad has cut off international flights. Iran and Turkey have moved to erase Kurdish control of border crossings.

Outgunned and outmanned by the Iraqi military, Kurdish fighters appeared to be in headlong retreat today. A senior commander of Kurdish forces defending oil fields outside the city of Dibis, about 30 miles northwest of Kirkuk, said in a telephone interview that his troops had pulled out on Oct. 16 as Iraqi troops closed in.

The commander, who asked not to be identified because he was not authorized to speak with journalists, said Kurdish forces, known as peshmerga, had received orders to leave Dibis from superiors in Irbil, the capital of the autonomous region.

Kurdish fighters and Iraqi government troops are both part of the U.S.-led coalition battling Islamic State militants in Iraq.

The Americans did not interfere with the Iraqi military’s takeover of the Kurdish-held areas. The coalition and the U.S. Embassy in Baghdad urged both sides to avoid violence and focus fighting the militants.

The United States had always made clear to Barzani that it opposed the referendum, saying it would foment ethnic conflict, destabilize Iraq and undermine the fight against the Islamic State. Baghdad took steps to isolate the landlocked Kurdish region after the referendum, with the help of Iran and Turkey, and then began the assault on oil-rich Kirkuk province early Monday.

U.S. troops were in the province but had no role in the Iraqi military operation, said Col. Ryan Dillon, the spokesman for the coalition in Baghdad.

The loss of the Kirkuk oil fields could cripple the Kurdish region’s economy, costing 70 percent of its daily oil production, said Luay al-Khatteeb, the director of the Iraq Energy Institute in Baghdad.

“You can’t sustain a state with just 30 percent of your oil production,” he said.

Kurdish operators produce 790,000 barrels a day, including 550,000 barrels from Kirkuk province and other contested areas, Khatteeb said. The region exports 590,000 barrels a day, with the remainder used for domestic refineries and consumption.

Oil analysts say the region has earned about $8 billion a year from oil exports. Baghdad, which has accused the Kurds of stealing the oil, cut off federal payments to the Kurdish region in 2014.

The Iraqi military triumph over the Kurds came as the coalition continued to battle Islamic State militants clinging to a strip of desert land and the border city of Qaim, in western Anbar province near the Syrian border. Iraqi forces, in some instances aided by Kurdish fighters, have driven the militants from most of Iraq since they took over nearly a third of the country three years ago.

Elsewhere in Iraq today, Iraqi militia fighters allied with government troops took control of disputed areas in and around Sinjar, a northern region populated by Yazidis, a religious minority. A Yazidi militia commander in Mosul said peshmerga fighters withdrew from the area as part of a negotiated agreement.

More than 2,000 Yazidis were massacred in 2014 by Islamic State militants who enslaved Yazidi women and girls. The city of Sinjar was liberated in 2015 by peshmerga fighters backed by U.S. airstrikes.

In the northern city of Mosul, a commander of Iraqi military units said in a telephone interview today that the Iraqi government was negotiating with Kurdish leaders on a Kurdish withdrawal from disputed areas around Mosul near the Kurdish autonomous region.

The commander said peshmerga forces had already withdrawn from some local areas, known as the Ninevah plains in Ninevah province. He asked not to be identified because he was not authorized to speak with journalists.

To the south, the Iraqi military command in Baghdad said Iraqi troops had taken over several disputed areas in Diyala province held since 2014 by peshmerga forces, who withdrew early today.

In a sign that life in the city of Kirkuk was returning to normal, hundreds of families — most of them Kurdish — who had fled the city as Iraqi forces entered on Oct. 16 began coming home.

Abadi has assured Kurdish civilians that they would be protected by Iraqi forces and federal and local police. Kirkuk, a multiethnic city of about 1 million, is roughly 45 percent Kurdish, 38 percent Arab, 15 percent Turkmens and 2 percent Christian.

Roads connecting Kirkuk to Baghdad and to Irbil, closed during the military operation, were reopened today.

“We are all Iraqis,” Maj. Mohammed Ismael, a commander with Iraqi government counterterrorism troops in Kirkuk, said in an interview. “Kirkuk is now back in the heart of Iraq.”

Ali Riyadh, 28, an Iraqi army soldier dining at an expensive restaurant in Kirkuk today, said, “We came to Kirkuk yesterday and today I’m having lunch in this nice place. It was easier than we expected.”

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