Turkey and the United States have joined forces in a campaign to drive Islamic State militants back from Turkey's southern border and cinch off the extremists' vital corridors for weapons and fighters.
The mission to create an Islamic State-free zone in northern Syria is still in the planning phase, U.S. officials said Monday, and the new strategy for combating the militant organization that has proclaimed a Muslim caliphate across Syrian and Iraqi territory was expected to be the subject of an urgent closed-door meeting of NATO allies Tuesday.
No U.S. or Turkish ground troops would be involved in the new effort, officials said.
U.S. officials have so far declined to establish a no-fly zone along Turkey's border with Syria, fearing American warplanes would be drawn deeper into Syria's 4-year-old civil war if they patrolled the region with sufficient frequency to ground Syrian President Bashar Assad's air forces. The bloody conflict has pitted dozens of armed factions against Assad's hobbled government.
But the evolving shift in military posture toward Islamic State in both Washington and Ankara appears likely to result in de facto aerial protection for Syrian rebel forces in the strategic border strip — although U.S. officials insist they will not formally establish a no-fly zone.
The plan, which officials say is still weeks away from completion, centers around Western- and Turkish-backed Syrian rebels controlling a nearly 70-by-60-mile buffer zone between the Euphrates River, at its eastern end, and the northern suburbs of Aleppo to the west. U.S. and Turkish warplanes would provide air support targeting Islamic State, which has slaughtered thousands of perceived enemies.
"Under consideration right now is deepening collaboration with our Turkish allies that's going to include air" strikes, said Pentagon spokesman Capt. Jeff Davis.
"This will ensure greater security and stability along the Turkish border with Syria and help overall coalition efforts to defeat ISIL in both Syria and Iraq," he said, using a common acronym for Islamic State.
Turkish President Recep Tayyip Erdogan also had been reluctant to take more aggressive action against Islamic State until recently, for fear that driving out the militants would strengthen Kurdish forces battling the extremists and tempt them into alliance with Kurdish insurgents in Turkey.
Turkish and U.S. officials emphasized that any ground operations would be left to the Syrian rebels but that they could count on the Western coalition's protection from the air.
"If we are not going to send land units to the ground — and we will not — then those forces acting as ground forces cooperating with us should be protected," Turkish Prime Minister Ahmet Davutoglu told journalists over the weekend, the Hurriyet newspaper reported.
"We don't want to see Daesh at our border," Davutoglu said, using an Arabic acronym for Islamic State.
The Obama administration has avoided use of the term "no-fly zone" for the planned buffer area, probably because a formal designation would require a vote by the U.N. Security Council, where Russia or China could use their veto power to block it. Russia is Assad's sole European ally, and China routinely opposes any action it interprets as the world body getting involved in a country's domestic affairs.
Turkey, though, wants U.S. air cover, as any success in clearing the border region of Islamic State gunmen could make the territory safe for resettlement by some of the 2 million Syrian refugees now sheltering in Turkey.
"Details remain to be worked out, but what we are talking about with Turkey is cooperating to support partners on the ground in northern Syria who are countering ISIL," said a senior administration official traveling with President Obama in Ethiopia on Monday.
"The goal is to establish an ISIL-free zone and ensure greater security and stability along Turkey's border with Syria," the official said, reiterating U.S. opposition to imposing a formal no-fly zone.
Ankara executed a significant shift in strategy last week when it began striking Islamic State targets in Syria and opened its Incirlik Air Base for U.S. air operations in the region.
Kurdish fighters now control much of the Syrian side of the border and have warned Ankara against intervening in the protracted war.
The Syrian Kurdish fighters, called the People's Protection Units, or YPG, are aligned with Turkey's Kurdistan Workers' Party, or PKK, which for decades has waged an insurgency in Turkey and is viewed by the Ankara government as a terrorist force on par with Islamic State.
"There is no difference between PKK and Daesh," Turkish Foreign Minister Mevlut Cavusoglu said during an official visit to Portugal on Monday. He said the PKK was involved in the fighting against Islamic State "for power, not for peace, not for security."
Airstrikes by Turkish warplanes in recent days have reportedly targeted Kurdish forces as well as Islamic State fighters, and the Syrian Kurdish militia accused Ankara of shelling its fighters on Monday near the border town of Jarabulus, a key crossing into Islamic State-controlled northern Syria for thousands of foreign fighters recruited by the militants through social media.
The reported Turkish attacks on Syrian Kurdish fighters could signal conflict within the emerging U.S.-Turkish mission because Washington is allied with Iraqi Kurdish forces and supportive of the Syrian YPG. The alleged targeting of the Syrian Kurds also could imperil the peace process launched in 2012 to end the PKK's insurgency, which has cost more than 40,000 lives over the last three decades.
Security officials in Ankara fear that a strengthening Syrian Kurdish presence on its southern border could give rise to a fresh PKK campaign for an independent Kurdish state.
But a July 20 suicide bombing in the Turkish border town of Suruc, which police blamed on Islamic State, killed 32 people and spurred angry demonstrations across Turkey. The protesters condemned both the attack and what is seen as the government's indifference to Islamist militants operating along the border with Syria.
"The geography is tailor-made for ISIS to exploit Turkish security vulnerabilities," Christopher Harmer, a military analyst at Washington's Institute for the Study of War think tank, said of Islamic State's latest targeting. "ISIS has tens of thousands of fighters willing to conduct suicide attacks." ISIS is yet another acronym for Islamic State.
Turkey invoked Article 4 of the North Atlantic Treaty Organization's founding documents to summon ambassadors of the 28-state alliance for an emergency meeting of the North Atlantic Council, its decision-making body, Tuesday in Brussels.
Ankara has not signaled that it will ask for alliance troops to tackle the threat, NATO Secretary-General Jens Stoltenberg said Monday.
"Turkey has a very strong army and very strong security forces so there has been no request for any substantial NATO military support," Stoltenberg told the BBC in an interview.
The Article 4 summons was only the fifth since NATO's 1949 founding. The last emergency gathering was called by Poland in March 2014 after Russia seized and annexed Ukraine's Crimean peninsula.
Williams reported from Los Angeles and Hennigan from Washington. Times staff writer Christi Parsons contributed to this report from Addis Ababa, Ethiopia.