The rebel source said it was "likely that (Al-Qaeda's Syria affiliate) Al-Nusra Front shot down the plane and took the pilot," adding that the plane had been hit by heavy machinegun fire.
The Syrian Observatory for Human Rights said Al-Nusra downed the plane, which it said was likely being flown by a Syrian air force pilot.
The Al-Qaeda affiliate is not party to the ceasefire between government forces and non-jihadist rebels brokered by the US and Russia that has been in place since February 27.
In video footage circulated on social media purporting to show the scene where the plane came down, a dozen men crowd around a man lying in the dirt.
Some of them cry: "He's Syrian, he's Syrian!" and others yell: "Get his weapons off him!"
AFP could not confirm the authenticity of the footage.
Last month, Islamist rebels shot down a regime warplane over the village of Kafr Nabuda in the central province of Hama.
