A video distributed on Friday appeared to show the execution on the orders of an Islamic court of a Syrian rebel leader and his aide in the northern city of Aleppo on charges of criminal activity.
The Syrian Observatory for Human Rights said the court had accused the pair shown in the video, which AFP has been unable to independently verify, of theft, murder and extortion.
The Britain-based Observatory said the execution took place on May 31.
The clip purports to show Mahmud Hussein al-Abed, chief of the rebel Mohammed's Army Brigade and his aide are shown kneeling and blindfolded in the open air.
Abed, with his long, grey beard, white prayer cap and combat fatigues listens as a rebel reads the accusations against him.
"You are accused of having... emptied the stores of medicines under the pretense of buying weapons, stolen cars on the basis that their owners are shabiha [pro-regime militia], given the order to kill a Jihadist, and incited the members [of the brigade] to steal," the voice says.
"Those who fight God and his prophet... should be killed, their hands and feet cut off," the rebel, whose voice never appears on camera, says, listing several other charges against the men.
Gunmen then open fire on the two men, and the camera shows their bodies after the shooting has stopped.
Several Islamist groups fighting the regime of President Bashar al-Assad have set up their own courts in areas they control and imposed punishments based on sharia (Islamic law).