A youth uses binoculars to look at Turkish army tanks holding positions, near the border with Syria, in the outskirts of the village of Elbeyi, east of the town of Kilis, in southeastern Turkey, Thursday, July 23. (Emrah Gurel/AP)

Turkey has agreed to let the United States use Turkish soil to launch air attacks against the Islamic State, signaling a major shift in policy on the part of the once-reluctant American ally, U.S. officials said Thursday.

The decision to allow U.S. warplanes to use the Incirlik air base in southern Turkey is one element in a broad cooperation plan first broached nine months ago. Additional elements — including expanding U.S. airstrikes into the western part of the border area and using Turkish military ground spotters to guide them — are being discussed and finalized.

Turkey had resisted being drawn too deeply into the war against the Islamic State because of concerns about the direction of the Obama administration’s Syria policy.

The Incirlik deal was sealed in a telephone conversation Wednesday between President Obama and Turkish President Recep Tayyip Erdogan, a senior U.S. administration official said, speaking on the condition of anonymity to discuss sensitive information.

A White House statement said only that the leaders had discussed “deepening our ongoing cooperation in the fight against ISIL, as well as common efforts to bring security and stability to Iraq and a political settlement to the conflict in Syria.” The Islamic State is also known as ISIS and ISIL.

File photo, a U.S. Air Force plane takes off from the Incirlik airbase, in southern Turkey. (Vadim Ghirda/AP)

Use of the Incirlik base, located just 60 miles from the northwest Syrian border, would enable piloted U.S. warplanes and armed drones to move more quickly and efficiently against Islamic State targets in their northern Syrian strongholds, U.S. officials have said. Planes currently fly from Iraq, to Syria’s east, and from Arab states such as Jordan and in the Persian Gulf region that are a part of the anti-Islamic State coalition.

Surveillance aircraft have been permitted to fly from Incirlik, but the Turkish government’s refusal to allow the base to be used for air attacks had triggered one of the deepest rifts in the U.S.-Turkish alliance in more than a decade, reflecting deep-seated policy differences between Ankara and Washington over ways to address the Syrian war. Incirlik has hosted American forces under the umbrella of the NATO alliance for many years, but it remains subject to Turkish sovereignty.

Turkish officials made no immediate comments, although several Turkish media outlets reported the Incirlik agreement. In a news conference Wednesday, Deputy Foreign Minister Bülent Arinç said Turkey had “agreed on certain topics to support the [anti-Islamic State] coalition’s efforts during a recent meeting with the U.S. special representative,” a reference to retired Gen. John R. Allen, the administration’s coordinator for the coalition, who visited Turkey earlier this month.

“A unanimity of thought and action has been reached about the issue of joint operations in the future,” Arinç said, according to the Hürriyet newspaper. “A related cabinet motion is now open for a signature.”

The newspaper quoted an unidentified U.S. official as saying that American strike operations from Incirlik will begin in August.

The agreement was reached amid heightened tensions on the Turkish-Syrian border. In their first significant ground engagement with the Islamic State, Turkish troops on Thursday fired artillery into militant territory near the Kilis border crossing, killing two fighters. The move followed what Turkish media reports said was an Islamic State attack on Turkish troops in the area that killed at least one Turkish soldier.

The shooting erupted after Turkey sought to prevent militant fighters from entering its territory illegally via one of the many smuggling routes used to ferry goods, supplies and people in and out of Syria, Turkish media said. The Turkish military said in a statement that it scrambled four F-16 fighters to the area to guard against a possible escalation.

The U.S.-Turkish talks already had picked up speed in recent weeks as the Islamic State increased its presence in northwestern Syria, moving beyond its strongholds in the eastern and central parts of the country in the direction of Aleppo, Syria’s largest city. The United States has in recent weeks carried out a growing number of attacks in the area.

Fighting in the northwest and in and around Aleppo has been primarily between Syrian opposition fighters and forces of President Bashar al-Assad’s government, and the United States has been reluctant to use its air power, which it has said is devoted solely to the fight against ISIS.

Under the plan, U.S. airstrikes could extend from Kobane, a Syrian town on the Turkish border, westward to the town of Azaz, about 20 miles north of Aleppo.

Whether Turkey has secured any concessions from the United States regarding its own concerns was not immediately clear. Turkey has repeatedly said it wants Washington to focus as much on removing Assad as on fighting the Islamic State. It also has said it wants a safe zone in the area, protected by air power, that would allow it to transfer back to Syria some of an estimated 2 million refugees on Turkish territory.

It was unclear whether the U.S.-Turkey arrangement under discussion would recognize any safe zone, but increased control of the 560-mile border would enhance efforts to prevent Islamist militants from crossing into Syria.

Significant gains by Syrian Kurds against the Islamic State in northern Syria to the east of Kobane also have contributed to the evolution of Turkey’s thinking. In recent weeks, Syrian Kurdish People’s Protection Units have seized large swaths of territory, consolidating Kurdish control over what Turkey fears represents the early outlines of a new Kurdish state.

The Kurdish advances have been aided by U.S. airstrikes, leaving Turkey at risk of losing out all along the border.

By aligning more closely with the U.S.-led coalition, Turkey may be seeking to forestall further Kurdish gains in the eastern border region and secure more robust support for the Syrian rebels in the west than would have been possible had it remained on the sidelines of the fight.

DeYoung reported from Washington. Missy Ryan in Amman, Jordan, and Hugh Naylor in Beirut contributed to this report.

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