ISTANBUL - With the United States continuing to pressure Turkey to do more in the fight against the Islamic State, Turkey's position has hardened around an idea it has pushed for years as a strategy to confront the chaos of the Syrian civil war: a buffer zone along its frontier with Syria.
The idea is emerging as a possible way to end the standoff between the United States and Turkey, and U.S. military planners are said to be looking at how to implement such a plan, which would require a no-fly zone and stepped up combat air patrols to take out Syrian air defense systems.
Yet the prospect of a buffer zone is proving deeply divisive in Washington, as it would go far beyond President Barack Obama's original mission of taking on the Islamic State and would lead to a direct confrontation with the Syrian government of President Bashar Assad.
While Turkey has largely described the plan in humanitarian terms - to protect refugees and also Turkey's border - the argument made privately is that a buffer zone would quickly evolve into a place where moderate rebels would be trained to fight Assad's government; in other words, a fledgling rebel state.
"It would mainly be a place where an alternate government structure would take root and for the training of rebels," said Frederic C. Hof, a senior fellow at the Atlantic Council and a former American envoy to the Syrian opposition.
Secretary of State John Kerry this week said the idea was "worth looking at very, very closely," and officials within the State Department have been pushing it. The Pentagon and the White House quickly disavowed it although they acknowledged having discussions about it.
Obama on Thursday dispatched the envoy coordinating the coalition against the Islamic State, retired Gen. John R. Allen, to Ankara, the capital, for two days of talks to nudge Turkey to play a greater role and go beyond what it is already doing - sharing intelligence and taking measures to control the flow of foreign jihadis traveling through Turkey.
But when Allen broaches the subject of direct military involvement, or even the use of an air base in Turkey, he is likely to be answered with a request for a buffer zone.
Jen Psaki, a State Department spokeswoman, said Thursday that Allen and Brett McGurk, a deputy special envoy, in their meeting with Turkish officials, "emphasized that urgent steps" are immediately required to degrade the Islamic State's military capabilities and ongoing ability to threaten the region."
She added that they also stressed that strengthening the moderate Syrian opposition "is crucial to any realistic and lasting political settlement of the Syrian crisis." The reluctance of Turkey's president, Recep Tayyip Erdogan, to do more to fight the militants has exasperated many U.S. officials, who see Turkish tanks positioned on their side of the border while Kobani, a Syrian Kurdish city, faces a massacre if American-led airstrikes fail to stall a militant offensive.
In comments that appeared to amplify the divide between the United States and Turkey, which has long been an important ally and is a member of NATO, the Turkish foreign minister, Mevlut Cavusoglu, said in a news conference Thursday that a condition of Turkey's participation in the coalition against the Islamic State is the buffer zone.
He reiterated Erdogan's primary goal of defeating the Assad government before the Islamic State.
"Tyranny and massacres will remain in the region as long as the Assad regime continues," Cavusoglu said.
Without going into specifics, he said that once a "common decision" is reached between Turkey and its NATO allies, "Turkey will not hold back from doing its part."
While the Islamic State's threat to the United States and the West is mainly hypothetical at this point and centered on future worries of foreign jihadis returning home to launch attacks, for Turkey the crisis has long been an immediate security threat.
In recent weeks, as the battle has raged over Kobani, mortar shells have been flying across Turkey's southern border with Syria.
In the last week, Kurds - enraged at Turkey's unwillingness to help their embattled brethren in Kobani - erupted in violent protests, forcing Ankara to deploy the military, impose curfews and close schools. Buildings were set alight, statues of Mustafa Kemal Ataturk, modern Turkey's revered founder, were destroyed, and more than 20 people were killed in fighting between various factions - Kurds, Islamists, and nationalists - that invoked memories of a troubled past that Turks thought they had moved beyond.
The scenes of chaos, at the border and in Turkey's Kurdish enclaves, are part of the same struggle as Erdogan navigates his own set of interests that are, in many ways, at odds with those of Obama and the international coalition he has assembled.
For Erdogan, who recently became president after more than a decade as prime minister leading the Islamist Justice and Development Party, recent events have highlighted a paradox of his career: As he has achieved more power and more prominence, many of his signal achievements have been diminished. Last summer's sweeping anti-government protests and the ensuing police crackdown tarnished his democratic credentials. A corruption scandal eviscerated an image of clean government he had put forward.
The crisis over the Islamic State, and Turkey's reluctance to intervene in Kobani or allow Kurdish fighters to cross its territory to join the fight, threatens to derail an ongoing peace process with Turkey's own Kurds, which had been seen as one of Erdogan's most important legacies. Erdogan has been constrained in aiding the Syrian Kurds because many of them are linked to the Kurdistan Workers' Party, or PKK, which has waged an insurgency on Turkish soil for more than three decades, violence that has claimed more than 30,000 lives.
Turkey, with American involvement, has tried to push the Syrian Kurds aligned with the PKK to join the fight against the Assad government, something the group has largely avoided doing as it focused on establishing autonomy within Syria. Those talks, if successful, could bring greater Turkish involvement in fighting the militants.
Another constraint on Erdogan is his position as a devout leader who came to power by mobilizing Turkey's religious Sunni Muslim masses. While there is little outward support in Turkey for the Sunni extremists, any military involvement would be perceived within some segments of society as siding with the West against Sunnis.
Ozgur Unluhisarcikli, the director of the Ankara office of the German Marshall Fund of the United States, a research organization, said anti-Western sentiment is so ingrained among some Turks that regardless of the militant's brutality, any campaign against it involving the United States is seen as "another Western crusade against Sunnis."
So far, Erdogan's primary condition for greater involvement in the fight against the Islamic State is for the United States-led coalition to do more to oust Assad, who many say has been a beneficiary of the U.S. airstrikes. The United States has said it will begin training moderate rebels in Saudi Arabia, but this is not enough for Turkey, which has demanded that the buffer zone be established in northern Syria.
Verda Ozer, a scholar at the Istanbul Policy Center and a columnist at the Turkish daily Hurriyet, said the buffer zone idea is "what the U.S. and Turkey mostly disagree on. The buffer zone is a topic where all the gaps between Turkey and the U.S. are reflected. It's like a micro-symbol of that strategic disconnect."
Some analysts say that Turkey's call for a buffer zone would allow it to forestall any bid for Kurdish autonomy within northern Syria, and the Kurds have opposed the idea.
"Turkey is ultimately using the no-fly zone and talk of taking part in the coalition against ISIS as a cover for seeking international legitimacy for what they actually want to do, which is to crush the Kurds," said Halil M. Karaveli, an expert on Turkey and a senior fellow at the Central Asia-Caucasus Institute in Stockholm.
Despite Turkey's reluctance to do more militarily, said Francis J. Ricciardone Jr., who until July was the American ambassador to Turkey and is now the director of the Atlantic Council's Rafik Hariri Center for the Middle East, it has significantly increased its support in other ways, such as intelligence sharing and cutting off the flow of terrorist financing.
"I would say we are getting a lot more than we were in the past," Ricciardone said.
"Are we satisfied? No," he added. "But we're working on it."