On Sunday, the Syrian Observatory for Human Rights, an opposition-backed monitoring group, said that fighters from the Islamic State of Iraq and Syria had beheaded two men from the Sheitaat tribe, in the Deir Ezzor village of Shaafa, on the banks of the Euphrates. It also said 19 other Sheitaat fighters had been executed by the group earlier in the week.

The Sheitaat have been described as a “pocket of resistance” to ISIS’s increasingly brutal methods of oppression in Syria’s eastern province. In recent weeks, ISIS has stepped up its intimidation campaign in areas that oppose their rule, with reports of beheadings and crucifixions.

Syria’s eastern tribes are considered the last group that could pose a serious threat to ISIS’s control of Deir Ezzor. Tribes make up about 15 percent of the Syrian population, with a vast number living in rural areas.

We asked Dawn Chatty, a social anthropologist at the University of Oxford and a prominent researcher of tribes in Syria and elsewhere in the Middle East, to weigh in on the developments.

Syria Deeply: What is the situation right now between ISIS and Deir Ezzor’s tribes?

Dawn Chatty: ISIS’s tribal relationship came to the forefront because of the newspaper articles that emerged about the [descendants] of one of the big lineages, the Sheitaat. Now there’s been some counter-publicity that’s been produced by ISIS to say that they’ve gone back and executed the Bedouin who led the uprising against them. I would imagine that there’s gong to be a bigger Bedouin reaction to get ISIS out of areas because they’re behaving now in ways the Bedouin won’t tolerate. In many of these village areas, the Bedouin have allowed ISIS to be in certain urban areas as long as they respect the Bedouin, and when they haven’t respected them, they’ve been fighting them.

ISIS has been very, very clever in the way it’s using social media and reporting facts that haven’t actually happened on the ground. I’m not sure you can [even confirm] the Sheitaat men have really been executed. It would be a very dangerous move for ISIS.

I’ve tried to say before – the tribes probably make up around 15 percent of the population of Syria, and in rural Syria, they are more than 15 percent. From the very beginning of the war, they have been active in defending their neighborhoods. The first armed opposition was by tribesmen who all had small arms, and very early on they were protecting their neighborhoods. No one has talked about where they’ve gone [since then] – into the badia, the desert, the areas the government doesn’t control. I think we’ll see more and more activity from the tribes because the more extreme ISIS becomes, the tribes who’ve agreed to live and let live won’t let that happen anymore. They seen ISIS’s recent behavior as totally immoral.

Syria Deeply: How prepared is ISIS to take on the tribes?

Chatty: I think that ISIS’s leadership is not particularly well-trained with the Bedouin. Obviously Baghdadi has some understanding about how the Bedouin operate. But many of the fighters are not from Syria or Iraq – there’s a lot of Chechen fighters and Circassians, and I don’t think you can say whether they’re superior or not. They’re extremists. I don’t think they care [if the Bedouin are well-equipped] – ISIS will control territory by terrorizing the local people. But the Bedouin are very hard to terrorize, and the Bedouin will really come back. I wouldn’t be surprised to see them come back and control Raqqa. ISIS almost walked into Raqqa and took it over without a fight because they made agreements with local tribes in the area. But now ISIS’s behavior is impacting the tribes and their economy and how they live, and they won’t accept it.

One of the things to keep thinking about is that tribes of the Sheitaat lineage are mostly opposed to the government. Then some of the Begara in Deir Ezzor were really disenfranchised under Hafez al-Assad and became very susceptible to Iranian Shia proselytization. Some converted to Shia Islam, which means there’s a point where they are going to see ISIS as being really dangerous for them, and I am sure that they’ll then form new alliances to get ISIS out of their area.

For now they’ll stay very quiet, and only say something when it starts to affect them personally. Then there are still some Bedouin tribal groups that are supporters of the regime, because so many of their men have been incorporated over the years into the security forces and the ministry of the interior. But I don’t think ISIS control [in tribal areas] here will be that strong. You’ll see the tribes start to gather up to fight.

Answers have been edited.