Human Rights Watch (HRW) reported Friday that groups of Syrian rebel forces executed at least 190 civilians and seized over 200 as hostages during a military offensive on August 4.
According to the report, a majority of the massacres took place in the city of Latakia, predominantly inhabited by members of Bashar al-Assad's minority Alawite sect.
“These abuses were not the actions of rogue fighters,” said Joe Stork, Acting Middle East Director at Human Rights Watch. “This operation was a coordinated, planned attack on the civilian population in these Alawite villages.”
Human Rights Watch says it conducted an on-site investigation and interviewed more than 35 people, including survivors and fighters from both sides of the offensive.
A 105-page report says that in the early hours of August 4, opposition fighters overran government positions in the Latakia countryside and occupied more than ten Alawite villages. HRW says it appears the civilians were killed on the first day of the operation.
The report says the high civilian death toll and the nature of the recorded wounds "indicate that opposition forces either intentionally or indiscriminately killed most of the remaining victims."
"The evidence strongly suggests that the killings, hostage taking, and other abuses committed by opposition forces on and after August 4 rise to the level of crimes against humanity," the report said.
HRW says Islamist rebel groups - which include foreign fighters - are financed by individuals in Kuwait and other Gulf states. It calls on the UN to impose an arms embargo on all groups credibly accused of war crimes.
Human rights organizations also accuse Syrian government forces of killing civilians during the country's 31-month long conflict, most recently in a poison gas attack near Damascus on August 21 in which hundreds died. President Bashar al-Assad denied the allegations saying it was rebel fighters who were responsible.
In a separate case of war crimes during the fighting in Syria, a group of Hezbollah fighters filmed themselves rejoicing and celebrating as they dragged injured Syrian civilians from a van and executed them.
Hezbollah has been fighting alongside Syrian army forces loyal to the regime of Bashar al-Assad, and have provided key support in a number of strategically important operations against rebel forces.