A video clip has emerged apparently showing Chechen fighters publicly slaughtering two people in Idlib, with some claiming one of those killed is one of two prominent bishops missing in Aleppo.
The execution, carried out in front of a crowd of people in the north of Syria, triggered a wave of anger from citizens and religious figures.
Others in the area have said the same Chechen group slaughtered a mercenary and poured his blood over another live man.
A local source from the town controlled by the group in Idlib countryside denied any relationship between the clip and the brigade, insisting it is "mere rumor, aimed at jihadists".
Meanwhile, opposition businessman Firas Tlass said he considered the brigade to be working against the revolution, accusing it of being sent by Russian intelligence.
Tlass, speaking on his personal Facebook page, asked the chief of the Military Council in Aleppo, Colonel Abdul Jabbar Ugaydi and the leader of the Tawhid Brigade, Abdul Kader Saleh, along with the leader of the Fatah division, Abu Bakr, to direct a force to expel the group's leader, Abu al-Banat and his mercenaries from Syria immediately, saying it was an urgent priority.
Sources have previously revealed that advice was provided by Russian intelligence to the Syrian regime to distort the image of the rebels and the Free Syrian Army by filming cruel scenes and broadcasting them as opposition crimes.
Observers say rebel crimes are being used as cover for more brutal crimes being committed by the regime in places like Banias, Bayda and Tal Kalakh.
Many sources have reported news that Chechen divisions are joining the rebels inside Syria, with some saying the divisions also include fighters from the Balkans.
Activists accuse the groups of serving the regime, believing they are recruited by Russian intelligence to work among the rebels and eliminate the field leaders of the Free Syrian Army.
Translated and edited by The Syrian Observer