ALEPPO, Syria — The sniper walked through the rubble near this city’s front lines. He was searching for another spot from where he might catch a Syrian soldier in his rifle scope’s cross hairs.

Speaking in French-accented English, he said he was not Syrian, but a roaming jihadist who had journeyed here to help the Sunni uprising against President Bashar al-Assad’s secular, Alawite rule.

“I am a Muslim,” he said. “When you see on TV many of your brothers and sisters being killed you have to go help them. This is an obligation in Islam.”

The presence of this foreign antigovernment fighter, who claimed to be from Paris and gave his name as Abu Abdullah, pointed to recurring questions of the battle for Syria’s largest city: How much longer will the fighting last, and what will its effects be?