The Islamic State militant group has executed 700 members of a tribe it has been battling in eastern Syria during the past two weeks, the majority of them civilians, a human rights monitoring group and activists said on Saturday.
The Syrian Observatory for Human Rights, which has tracked violence on all sides of the three-year conflict, said reliable sources had reported that beheadings were used to execute many of the al-Sheitaat tribe, which is native to Deir al-Zor province.
The conflict between Islamic State fighters and the al-Sheitaat tribe, who number about 70,000, flared after the militants took over two oil fields in July.
"Those who were executed are all al-Sheitaat," Observatory director Rami Abdelrahman said by telephone from Britain. "Some were arrested, judged and then killed."
After proclaiming a "caliphate" straddling parts of Iraq and Syria, the Islamic State has swept across northern Iraq in recent weeks, pushing back Kurdish forces and driving tens of thousands of Muslims, Christians and members of the Yazidi religious minority from their homes, prompting the first U.S. airstrikes in Iraq since the withdrawal of American troops in 2011.
The insurgents are also tightening their grip in Syria, of which they now control roughly a third, mostly rural areas in the north and east.
An activist in Deir al-Zor who spoke on condition of anonymity said 300 men were executed in one day in the town of Ghraneij, one of the three main towns of the al-Sheitaat tribal heartland, when Islamic State stormed the town.
Another opposition activist from Deir al-Zor said residents of al-Sheitaat towns had been given three days to leave.
"Those who were executed during the storming of the al-Sheitaat area are around 300. The rest were killed in the course of the battles," he said.
Tribal powers in Syria and Iraq have had to make the choice between fighting Islamic State or pledging allegiance.
On Friday, a video posted on YouTube showed men who said they were from the al-Sheitaat towns of Kishkeih and Abu Hammam pledging full support to the Islamic State.
"We say that what Islamic State stands for is justice," a tribal member sitting in a room with dozens of other men said in a statement.
The head of the al-Sheitaat tribe, Sheikh Rafaa Aakla al-Raju, called for other tribes to join the fight against the militants in a recent YouTube video.
"We appeal to the other tribes to stand by us because it will be their turn next. . . . If (Islamic State) are done with us the other tribes, will be targeted after al-Sheitaat. They are the next target," he said.
With your current subscription plan you can comment on stories. However, before writing your first comment, please create a display name in the Profile section of your subscriber account page.