U.S., Turkey weigh which Syrian rebels to support in border area

By Phil Stewart and Warren Strobel WASHINGTON (Reuters) - The United States and Turkey have not yet agreed which Syrian rebels they will support in a joint effort to help clear Islamic State from an area along the Turkish border, officials said on Tuesday, underscoring uncertainty surrounding the campaign plan. Washington and Ankara this week announced their intention to provide air cover for Syrian rebels and jointly sweep Islamic State fighters from a strip of land along the border, with U.S. warplanes using bases in Turkey for strikes. But planning appears to be just getting under way and resolving crucial details, like which opposition groups will be supported on the ground, could stoke longstanding tensions between the United States and Turkey about Syria strategy. Also still to be resolved in talks with Turkey, officials say, are how deep into Syria the area might extend and how quickly U.S. warplanes will begin flying combat missions from Turkish bases. President Barack Obama's administration, wary of being dragged into Syria's messy civil war, has so far struggled to find enough partners on the ground to help claw back territory from Islamic State, relying heavily on Kurdish fighters. Turkey, in turn, is wary of Kurdish fighters and might be less concerned than Washington about groups with some extremist links or with ambitions to broaden the fight to toppling Syrian President Bashar al-Assad. "We have to sit down with the Turks and figure it out," a senior Obama administration official said in a briefing with reporters, speaking on condition of anonymity. The official acknowledged there were opposition groups in Syria "we absolutely will not work with." The U.S. military has so far only trained about 60 Syrian rebel fighters, far below expectations, thanks in part to strict vetting requirements that, for example, weed out fighters whose primary aim is to overthrow Assad. Derek Chollet, who was an assistant secretary of defence under the Obama administration, said decisions about which groups to support will never be easy and noted longstanding differences between Washington and Ankara over Syria strategy. "While our cooperation has steadily improved and the urgent crisis seems to have pushed us even closer, our differences are likely masked rather than fully resolved," Chollet, now a senior adviser at the German Marshall Fund, said. TURKEY AND BORDER ZONE The most powerful insurgent groups operating in northern Syria include the al Qaeda-linked Nusra Front and the conservative Islamist Ahrar al-Sham, which has in recent weeks published two op-eds refuting the idea it is part of al Qaeda. Both are part of an insurgent alliance which, with Turkish support, has seized much of Idlib province in recent months. There are also an array of smaller groups operating in and around the northern city of Aleppo, some of which still fight under the banner of the "Free Syrian Army". Syrian rebels say driving Islamic State from areas near Aleppo would allow them to focus their efforts on fighting Assad. They mostly welcome the idea of a buffer zone where they could operate free from the risk of Syrian air strikes. "We are now mixing hopes with expectations," said Ahmad Qura Ali, a spokesman for Ahrar al-Sham. "We hope it won't take time and our expectation is that it won't take a long period perhaps a few months," he added. But questions over the scope of the zone are a source of concern for some. One rebel commander said a buffer zone would be counterproductive if it did not include cities. The result might be to encourage civilians to flee from other opposition-held areas - an outcome that would play to Assad's advantage. "We want international protection for areas that are inhabited, for the cities. I advise them to focus on protecting the cities," said the commander, who declined to be identified due to the political sensitivities of his criticism. Robert Ford, a former U.S. ambassador to Syria, said Turkey would likely have the greater say on security arrangements in the zone near its border, partly because of its proximity. Ford, now at the Middle East Institute, said Washington will not work with Nusra Front. But as for less hardline Islamist groups, "I guess the administration can live with that," he said. One group Turkey is not expected to welcome into the zone are the Kurdish YPG militia, which has pushed back Islamic State with the help of U.S.-led air strikes in northern Syria. Ankara has started striking militants from the Kurdistan Workers Party (PKK) in Iraq in recent days in response to attacks against its police officers and soldiers. But Turkish officials have said Turkish military operations in northern Syria are targeting only Islamic State and not Kurdish forces. (Additional reporting by Nick Tattersall in Istanbul and Suleiman al-Khalidi and Tom Perry in Beirut; Editing by Cynthia Osterman, Janet McBride)