As violence grows in Syria, many warn it could turn sectarian.
"If things do not change, the future is likely to be one of brutal repression, massacres, sectarian violence, and even all-out civil war," international envoy Kofi Annan warned at the UN recently. "All Syrians will lose."
But there are signs a sectarian conflict is already under way.
The clearest: the visibility of the Shabiha militia. Drawn entirely from the Alawite sect of the ruling Assad family, it is suspected of responsibility for the Houla massacre that left 108 dead, including 49 children, on May 25-26.
UN officials have expressed "strong suspicions" about the militia's role in the massacre due to survivors' accounts. Witnesses say the killing in Houla, a Sunni hamlet, opened with troops shelling homes but began in earnest with the arrival of hundreds of armed civilians from nearby Alawite villages.
Fabrice Balanche, director of the French research center Gremmo, says the witness accounts, if proven, would be the strongest evidence to date of communal warfare. But he says the pattern for hostilities is already well established.
"Since September 2011 at Homs, we have seen that it is a sectarian war," Balanche says. "You have the Syrian Army fighting against the opposition, but the opposition is only Sunni people. You have very few non-Sunni people in the Free Syrian Army. I think there is no Alawi, no Christian in the Free Syrian Army. And in front of them you have the Syrian Army and in Homs most of the Syrian soldiers were from the Alawite community."
The Alawites, who split from the Shi'ite branch of Islam in the ninth century, make up some 12 percent of the Syrian population but hold sway through their domination of the government and army.
Balanche, who has researched the Alawite rise to power, says communal tensions are greatest along the border lines between distinctly Alawite and Sunni areas of the country.
But even in major cities, the Shabiha plays a front-line role in bolstering the regime. Members of the Shabiha, who usually wear white trainers and are fully armed, beat and shoot protesters despite having no official powers.
The Shabiha -- which means "ghosts" -- date back to the time of Assad's father, Hafez, who seized power in a 1970 coup and introduced Alawite rule. Just how centrally controlled is the militia is a subject of much speculation.
One reason for mystery is that the militia is not a standing organization. Balanche says it coalesces as needed from among poorer Alawite youths and men when the call is put out by relatives who work for the intelligence or military. The vigilantes are paid by the regime or simply allowed to keep what they loot.
The Syrian regime appears to regard the Shabiha as valuable for two reasons.
One is the regime's own uncertainty about the loyalty of all its army units. Balanche says those worries require Damascus to use just one army corps, the Fourth Division commanded by Bashar's brother, to do the fighting in restive Homs Province.
"The Fourth Division, led by Maher Assad, is exclusively Alawite; there is no Sunni, no Christian, no Druze in this corps, and this Fourth Division is used by the regime against the resistance very strictly," Balanche says. "The Sunni battalions are in other areas where it is less dangerous because the regime is not sure about the fidelity of the Sunni soldiers."
The manpower reserves of the Shabiha, which activists say fight beside the Fourth Division, afford the regime the ability to choose which army units to deploy.
But another reason the Shabiha is useful is that it presumably offers the government some distance from atrocities.
As international observers said this month they suspected militiamen in the Houla massacre, Damascus said the civilian clothes proved the killers were not government forces. Instead, it blamed antigovernment provocateurs.