US and Turkey have agreed to a plan to root out IS from a strip of Syrian territory along the Turkish border, a plan that could lead to a a safe haven for tens of thousands of displaced Syrians but one that also sets up a potential conflict with US-backed Syrian Kurdish forces in the area.
The move further embroils Turkey, a key NATO ally, in Syria's civil war. It also catapults it into a front-line position in the global war against IS.
A senior Obama administration official said on Monday that US discussions with Turkey about an IS-free zone focused on a 68-mile stretch still under IS control. The US has been conducting airstrikes there, which will accelerate now that the US can launch strikes from Turkish soil, the official said.
No agreement between Turkey and the US has yet been finalized, said the official, who spoke on condition of anonymity under regulations.
In Washington, State Department spokesman John Kirby said that any joint military efforts with Turkey would not include the imposition of a no-fly zone. The US has long rejected Turkish and other requests for a no-fly zone to halt Syrian government air raids, fearing it would draw US forces further into the civil war.
While details of the buffer-zone plan have yet to be announced, Turkish Prime Minister Ahmet Davutoglu said Ankara and Washington have no intention of sending ground troops into Syria but wanted to see Syria's moderate opposition forces replace IS near the Turkish border.
"Moderate forces like the Free Syrian Army will be strengthened, a structure will be created so that they can take control of areas freed from ISIL, air cover will be provided. It would be impossible for them to take control of the area without it," Davutoglu told Turkey's A Haber television. ISIL is an alternate acronym for the Islamic State group.
The discussions came amid a major tactical shift in Turkey's approach to IS. After months of reluctance, Turkish warplanes started striking militant targets in Syria last week, and allowed the US to launch its own strikes from Turkey's strategically located Incirlik Air Base.
Turkey has also called a meeting of its NATO allies for Tuesday to discuss threats to its security and its airstrikes. Davutoglu said "NATO has a duty to protect" Turkey's border with Syria and Iraq, and that Ankara will seek the alliance's support for its actions at the meeting in Brussels.
But a Turkish-driven military campaign to push IS out of territory along the Turkish border is likely to complicate matters on the ground.
US-backed Kurdish fighters in Syria, who have been the most successful in the war against IS, control most of the 910 kilometers (565 miles) boundary with Turkey, and have warned Ankara against any military intervention in northern Syria.
The Islamic State controls roughly a 60-mile stretch of that border, wedged between Turkish-backed insurgents with Islamist ideologies to the left and Kurdish forces from the People's Protection Unit, known as the YPG, to the right.
The Turkish-US plan raises the question of which Syrian rebel forces would be involved in a ground operation against IS. The US has long complained about having no reliable partners among them. Defense Secretary Ash Carter acknowledged earlier this month that the US has only 60 trainees in a program to prepare and arm thousands of moderate Syrian rebels in the fight against IS militants.
The Obama administration official said the US-led coalition was looking to anti-IS forces such as Syrian Kurds and the Free Syrian Army. He did not elaborate
Syria's main Kurdish militia - the YPG or the People's Protection Units - is affiliated with the Kurdistan Workers' Party, or PKK, which has waged a decades-long insurgency in Turkey and maintains bases in remote parts of northern Iraq.
Nawaf Khalil, head of the Germany-based Kurdish Center for Studies, said Ankara is likely trying to limit advances by the Syrian Kurdish forces by using the war against IS as a pretext and to steer Washington away from the YPG, but "this will not work."
In a reflection of the complexities involved, Turkish Foreign Minister Mevlut Cavusoglu on Monday refused to draw a distinction between the Islamic State group and the PKK.
"There is no difference between PKK and Daesh," Cavusoglu said, using the Arabic acronym for Islamic State group. The PKK is fighting the IS "for power, not for peace, not for security," he said.
Kirby, the State Department spokesman, said "Turkey has a right to defend itself" against the PKK.
In a series of cross border strikes since Friday, Turkey has not only targeted the IS group but also Kurdish fighters affiliated with forces battling the extremists in Syria and Iraq.
Also, the YPG and an activist group said Turkish troops had shelled the Syrian border village of Til Findire, targeting Kurdish fighters and hitting one of their vehicles on Sunday night. The village is east of the border town of Kobani, where the Kurds handed a major defeat to the Islamic State group earlier this year.
But Turkish officials dismissed the claims, insisting their forces were only targeting the IS group in Syria, and the PKK in neighboring Iraq.
An Ankara official said Turkey returned fire after Turkish soldiers at the border were fired upon, in line with Turkey's rules of engagement.
"The Syrian Kurds are not a target of the operations. Our operations only target IS in Syria and PKK in Iraq," he said, speaking on condition of anonymity because of rules that bar officials from speaking to journalists without authorization.
Late on Monday, a major in Turkey's military police died after suspected PKK militants fired on his car in the southeastern province of Mus, said the region's governor, Vedat Buyukersoy. The major was among the highest ranking Turkish officers to be killed in attacks in recent years.
Turkish police raided homes in a neighborhood in the capital earlier in the day, detaining at least 15 people suspected of links to the Islamic State group, the Turkish state-run news agency said. The number of suspects detained in a major anti-terror operation launched on Friday has reached 1,050, according to the office of Turkey's prime minister.
However, in the absence of a no-fly zone to neutralize Syrian President Bashar Assad's warplanes, it is not clear how the possible buffer zone may be considered a safe haven where displaced people could return.
And despite the US and Turkey's shared interests in fighting the Islamic State, the Turks have also prioritized defeating Assad. While the US says Assad has lost legitimacy, it has not taken direct military action to try to remove him from office and says he is not the target of its efforts in Syria.
Ege Seckin, a Turkey expert at IHS Country Risk, said IS is a national security threat for Turkey, but was nonetheless secondary.
"The two key points in Turkey remain: one - topple the Assad regime, and two - prevent the establishment of a continuous Kurdish territorial entity in the region," he said.