Syrian rebels pose after seizing control of the Bab al-Hawa border post on the Syrian-Turkey border on July 20. Now, the rebels are facing a new challenge: radical Islamists, who they say do not represent them. Bulent Kilic/AFP/Getty Images hide caption

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Rebel fighters take up position near the military airport outside the rebel-held town of Azaz in northern Syria on Aug. 21. In rebel-held towns like Azaz, activists are taking on new, risky roles as the uprising against Syrian President Bashar Assad continues. Youssef Boudlal/Reuters/Landov hide caption

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Syrian rebels captured the Bab al-Salam crossing on the border with Turkey in July. Large numbers of refugees fleeing northern Syria for Turkey come to the crossing, which is orderly and well-run, at least for now. Adem Altan/AFP/Getty Images hide caption

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Syrians gather by the rubble of a house destroyed by shelling in the northern town of Azaz, on the outskirts of Aleppo, on Monday. Muhammed Muheisen/AP hide caption

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Syrians take refuge Thursday at the Bab Al-Salameh border crossing near the Syrian town of Azaz, in hopes of entering one of the refugee camps in Turkey. Muhammed Muheisen/AP hide caption

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Syrian children, who fled their home with their family, take refuge at the Bab Al-Salameh border crossing, in hopes of entering one of the refugee camps in Turkey on Sunday. Muhammed Muheisen/AP hide caption

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The daily fighting in Syria included this gun battle Wednesday involving rebels in the northern city of Aleppo. Still, the rival sides recently worked out a prisoner swap in which two women were freed from state custody, while the rebels released seven pro-government fighters. James Lawler Duggan/AFP/Getty Images hide caption

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Syrians fleeing increased violence arriving last week at the border between the Syrian town of Azaz and the neighboring Turkish town of Kilis. Phil Moore/AFP/Getty Images hide caption

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Members of the group Hamza Abdualmuttalib trained this week near the Syrian city of Aleppo. Bulent Kilic/AFP/Getty Images hide caption

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Syria's ongoing fighting is increasingly a sectarian conflict with the majority Sunni Muslims facing off against the Alawites who make up most of the country's ruling elite. Here, government opponents rally in the northern town of Mareh on June 29. Vedat Xhymshit/AFP/Getty Images hide caption

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