The ghosts appear in grainy videos as leering dogs of war, with steroidal biceps and tattoos declaring their loyalty to the Syrian regime. They surface more frequently every week as the civil war intensifies, in the stories of villagers who dare to speak about the bearded men who ransack homes and execute children in their bedrooms.
Locals call them shabiha, an Arabic word derived from "ghost," but even the origins of the term are disputed. Thugs, gangsters, militiamen; whatever they're called, experts and Syrian activists say that roving bands of plainclothes gunmen are playing an increasing role in the brutal suppression of dissent.
Nobody knows precisely why Damascus has turned to pro-government militias for the dirtiest tasks in the war. Some suggest that using informal forces gives the regime deniability; others say the militias are more willing than regular troops to kill unarmed victims. The darkest speculation suggests that the Syrian government is sending gangs of Alawites, a Shia sect, to slaughter rebellious Sunnis – intentionally reigniting the ancient struggle between the Shia and Sunni branches of Islam, the sectarian equivalent of scorched-earth strategy.
This is part of a bloody tradition, just one among hundreds of examples in recent decades of strongmen provoking ethnic or religious hatred to muster forces in defence of their regimes. But it's a particularly dangerous strategy in the tinderbox of Syria, where activists fear that the shabiha provocateurs could tip the country into a grassroots sectarian conflict, pitting the 74-per-cent Sunni majority against the wealthier Alawite minority. Such a conflagration could engulf a region where Shia and Sunni states – Iran, Saudi Arabia, Qatar – already stand accused of using Syria as a proxy battlefield.
"This is still not a sectarian war, although it's very close," said Hassan Hachimi, 48, a member of the Secretariat-General that leads the Syrian National Council, an umbrella group for the opposition.
The SNC has fought the impression that the uprising consists only of Sunni rebels and recently appointing a Syrian-Canadian, Tawfik Dunia, as the first Alawite on the group's executive. The SNC also elected a Kurdish academic, Abdulbaset Sieda, to serve as president.
But these efforts to cobble together a national movement, which includes all of Syria's demographic factions, have crashed against the reality of the battlefield. The United Nations reported this week that the rebels are gaining territory and experts say these gains have hardened support for the regime among Alawite volunteers. The sect enjoyed economic advantages since Hafez al-Assad took power in 1971 and now some Alawites are signing up to fight for Mr. al-Assad's son, Bashar. Every advance by Sunni rebel brigades increases the number of Alawites who become shabiha.
"The Alawites are fighting for their own security now," said Fabrice Balanche, director of the French research centre Gremmo. He put the number of shabiha at perhaps 100,000 men, although other experts say it's impossible to guess the size of a nebulous force.
Whatever their true numbers, they appear to have evolved rapidly from their roots as a loose network of criminals around the port city of Latakia. Starting in the 1970s, activists say, the shabiha emerged as a series of gangs that served as unofficial gunmen for the Assad regime. Security forces seemed to give them wide latitude for smuggling, thievery, blackmail and robbery.
"They were involved in dirty business, mostly smuggling drugs and cigarettes into the port," said Omar Muqdad, 32, an independent Syrian activist. "Now we have local shabiha in many parts of the country."
Shabiha helped the security forces suppress demonstrations when they flared up last year, initially attacking protesters with sticks, knives, electric prods and metal chains. Now they appear to have graduated to more systematic killing, reportedly mowing down whole villages with automatic gunfire and setting them on fire.
Some estimates put the deaths in Syria at 15,000 so far, a staggeringly high number, but also an indicator cited by activists to support their argument that the country of 20 million has not yet descended into an outright sectarian war. A clash between Alawites and Sunnis, village against village, could produce a vastly higher toll.
Nor do the shabiha militias appear to be entirely out of control, independently rising up against the rebellion. Donatella Rovera, a senior adviser at Amnesty International who spent weeks inside Syria to research her latest report, witnessed the shabiha in three parts of the country – and in each location, she said, the militiamen were working shoulder-to-shoulder with Syria's regular forces.
Ms. Rovera saw them travelling together in trucks and buses, and even firing on crowds in Aleppo. Such co-operation suggests that the shabiha obey orders from Damascus, rather than following a spontaneous tit-for-tat cycle of revenge, she said.
"It's not yet one village against the other," Ms. Rovera said. "There's been remarkably little of that, under the circumstances."
Reports from UN observers have supported the notion that many of Syria's massacres so far have resulted from cold-blooded calculation. When pro-government forces swarmed into villages around Houla on May 25, shooting entire families dead in their houses, the attack was preceded by a barrage of heavy weapons from the Syrian army. The United Nations later estimated that the indirect fire killed no more than 20 of the 108 victims that day; in other words, the shabiha inflicted most of the carnage.
Civil wars such as the Syrian conflict have become far more common than wars between nations and struggles for colonial independence during the last half-century. When faced with internal threats, many governments have turned to militias for extra muscle; one study counted at least 350 such pro-regime militias over the last three decades.
Analysis by researchers from University of Mannheim and the University College London found that human-rights violations such as torture, extrajudicial killing, political imprisonment and disappearances were far more common in places where pro-government militias operated, and especially when those militias were semi-official.
The rising prominence of the shabiha has raised concerns that Syria will follow the pattern of the Balkans, with British Foreign Secretary William Hague warning this week that the country could become "the next Bosnia." Mr. Balanche, the French academic, said that he has been writing for a decade about how Syria's patchwork of ethnic and sectarian groups threatens to break up the country. He warned that the regime's collapse could fragment the state into an Alawite enclave on the coast, a Kurdish state in the mountainous north and a Sunni zone surrounding the desert interior.
"If Assad falls, Syria will explode," Mr. Balanche said.
Syrian activists say they are acutely aware of the dangers. For the sake of their country, they say, it's vitally important that the revolutionaries avoid rising to the shabiha 's provocation.
"The regime is trying to lead us into a sectarian war," Mr. Muqdad said. "There have been a lot of massacres, so you can see some reaction starting. The ruling clique doesn't care about any religion but not all the people on the ground know this. They just know Alawites are trying to kill us."