BEIRUT - More than 230 bodies of people believed killed by Islamic State militants have been found in a mass grave in Syria's eastern Deir al-Zor province, activists said on Wednesday.
The bodies were thought to be members of the al-Sheitaat tribe which had battled Islamic State militants, the British-based Syrian Observatory for Human Rights and activists monitoring the conflict said.
Their deaths would bring the number of Sheitaat members said to have been killed by the ultra-hardline Islamist group to over 900.
Omar Abu Layla, a spokesman for the moderate rebel umbrella Free Syrian Army group in Syria's east, said Sheitaat tribespeople had discovered the mass grave as they returned to their homes. Islamic State, occupying the area, had given them permission to return.
"This is a message from Daesh that if there is any attempt at revenge, your fate will be the same as your relatives," he said, using a derogatory Arabic acronym for the Islamic State group.
Pictures shared by Abu Layla and activists on social media said to be of the mass grave showed decaying bodies and bones covered in dust and dirt lying amid rocks and sand.
Islamic State militants control all but a few pockets of Deir al-Zor province, which borders territory also under its control in Iraq.
The province's oilfields have been a major source of revenue for the group, but its operations have been under pressure since a US-led coalition started launching air strikes against it in Syria in September.