Typically: in every UN report on Syria, violations and war crimes by Syrian rebels are always placed at the end and always in passing (and with tons of qualifications)

"The report singles out extremist groups fighting the government, in particular the Islamic State of Iraq and Syria, which was blockading a town called Ar Raqqah. The United Nations said it also received unconfirmed reports of attacks on homes and churches after a strike on Latakia, on the Turkey-Syria border, by the Nusra Front, another extremist group."