The night before leaving his parents’ home in Wayne, Tex., to join the rebels trying to overthrow President Bashar al-Assad in Syria, Obaida Hitto left a bouquet of white roses for his mother, with a sterling silver locket and a note: “You’ve made me what I am. But now I need to go and do what I need to do.”

Mr. Hitto, 25, a former high school football player, deferred his plans for law school to sneak into Syria to assist the rebels by making videos and spreading information on the Internet to help their cause.

“I’m one of them,” Mr. Hitto said proudly during a recent telephone interview.

Since the early days of the uprising, Syrian rebel forces have filled their ranks with army defectors and civilians. But as the war has dragged on, and the government has made it much harder for soldiers to defect, two other groups have contributed to the opposition. There has been a rise in the number of foreign fighters, many of them Islamist extremists. But there has also been a small, though noticeable, number of men like Mr. Hitto, of Syrian descent and with Western passports, who have made the journey to join the Free Syrian Army. Experts estimate they number roughly a hundred and come from the United States, Britain, France and Canada.

Their presence is not enough to shift the tide of the battle, but they add another element of determination and complexity to a bloody landscape where loyalties and ambitions are often unclear.