The result is that the extremists face little immediate threat of an uprising by the tribes, which are traditionally the most powerful social institution in the large areas of eastern Syria and northern and western Iraq controlled by the group.

Any U.S. drive to try to turn tribesmen against the militants, as the Americans did with Sunnis during the Iraq war, faces an uphill battle.

Some tribes in Syria and Iraq already oppose the ISIS group. For example, the Shammar tribe, which spans the countries' border, has fought alongside Kurdish forces against the extremists in Iraq.

The U.S. and Iraqi governments have proposed creating a National Guard program that would arm and pay tribesmen to fight, though the effort has yet to get off the ground.

But in Syria in particular, tribes have no outside patron to bankroll or arm them to take on “IS”, leaving them with few options other than to bend to ISIS domination or flee.

“There are people who want to go back and fight them,'' said Hassan Hassan, an analyst with the Delma Institute in Abu Dhabi. "But the circumstances now mean that you can't provoke ISIS because the strategy they've followed and tactics are to prevent any revolt from inside.''

Divide and Rule

The rulers of the self-styled caliphate have mastered techniques of divide and rule. Tribes are powerful institutions that command the loyalty of their members across the largely desert regions of Syria and Iraq.

But they are also far from cohesive. Large tribes are divided up into smaller sub-tribes and clans that can be pitted against each other. Such divisions also emerge on their own, often in connection to control over local resources like oil wells or land.

Iraqi tribesmen, fighting alongside Iraqi police forces, pray as they hold a position in the Eastern part of Ramadi, West of the capital Baghdad.

Also, as AP correspondent in Beirut says, the ISIS group itself has roots in the tribes. Though hundreds of foreign fighters have flocked to join the group, most of its leaders and foot soldiers are Iraqis and Syrians and often belong to tribes.

In eastern Syria's Deir el-Zour province, for example, the Ogeidat is one of the largest tribes. One of its major clans, the Bu Jamel, has been a staunch opponent of the extremists. Another, the Bakir, long ago allied itself to the group.

IS operatives use threats or offers of money or fuel to win public pledges of loyalty from senior tribal Sheikhs. The group has also wooed younger tribesmen with economic enticements and promises of positions within IS, undermining the traditional power structure of the tribe.

"They offer many sweeteners,'' said Abu Ali al-Badie, a tribal leader from the central city of Palmyra in Syria's Homs province. "They go to the tribes and say, `Why are you fighting against Muslims? We'll give you weapons and cars and guns, and we'll fight together.''

"They offer diesel and fuel. They bring barley and animal feed from Iraq,'' he said. "They build wells at their own expense for the tribes and they say, “thers have neglected your needs.''

In Syria, IS has won the acceptance of some tribesmen in Raqqa and Deir el-Zour provinces by ending chaos that reigned when the areas were controlled by a patchwork of rebel warlords.

IS provides services including electricity, fuel, water and telephone lines, as well as flour for bakeries, said Haian Dukhan, a researcher at the University of St. Andrews Center for Syrian Studies.

"Things have started to become stable to a degree, and this is something that people were really desperate about,'' said Dukhan.

The group has "tribal affairs'' officials to handle relations with the tribes, calibrating its style to local dynamics. Often they will allow loyal tribesmen to run their communities' services, said Hassan.

The group also has removed its own commanders who caused tension with tribes in their areas. The idea, Hassan said, is ``to remove some of the toxins.''At the same time, the group sends a clear message to those who resist.

In August, IS militants shot and beheaded hundreds of members of the Shueitat tribe in eastern Syria. Activists reported death tolls ranging from 200 to 700.

Photographs in the ISIS’s English-language “Dabiq” magazine showed black-clad fighters shooting prisoners said to be Shueitat, lined up on the sandy ground.

ISIS militants have killed more than 300 members of Iraqi Albu Nimr tribe in western Anbar province, including dozens of women and children.

In Iraq, IS killed more than 200 men, women and children from the Al Bu Nimr tribe in Anbar province, apparently in revenge for the tribe's siding with security forces.
It has also shot dead several men from the Al Bu Fahd tribe.

"Everyone is hiding or fled. They will chop us in pieces if they see us,'' said Sheikh Naim al-Gaoud, a leader in the Al Bu Nimr. "They want us to support them and to join their fight. In return, they say they will let us live in peace.''

As a result, Dukhan says there's little chance for a revolt unless tribes are confident the extremists are losing. "I think that for the time being, seeing a large-scale uprising against IS is just a fantasy.''