The swaggering gunmen operate as hired muscle for the Syrian regime, clutching rifles and daggers as they sweep through towns and villages, sometimes after regular military troops have pulled back.
Recruited from the ruling elite's Alawite sect, the pro-regime militiamen known as "shabiha" are believed to be carrying out some of the most ghastly attacks of the Syrian uprising, allowing President Bashar Assad's government to deny direct responsibility for the crimes.
The U.N. says there are strong suspicions that pro-Assad fighters were responsible for at least some of the carnage during a weekend massacre in Houla, bringing fresh attention to the shadowy fighters who appear to be taking on a bigger role in Syria's bloody conflict.
More than 100 people were killed in the massacre, many of them women and children who were gunned down in their homes. Damascus has unequivocally denied any role, blaming the slaughter on terrorists _ the same term it uses for rebel forces in the country.
Many Syrians say the shabiha are more terrifying than the army and security forces, whose tactics include shelling residential neighborhoods and firing on protesters. The gunmen, they say, are deployed specifically to brutalize and intimidate Assad's opponents.
The origin of the word shabiha is murky, although some have speculated it comes from "shabah," the Arabic word for "ghost." Others say it signifies someone with a "long reach."
In a recent report on the shabiha, Syrian writer Yassin al-Haj Salih described the fighters as "spare muscle clutching a gun." Their privileges, he said, include "immunity, promotion, preferences at schools and universities, not to mention direct wages, such as the booty acquired in fighting the current revolution."
Even if the shabiha are responsible for Houla, however, there is no clear evidence that the regime ordered the massacre. There is no obvious chain of command from the regime to the shabiha, and it is difficult to assign blame for much of the country's bloodshed because the violence has become so widespread and chaotic.
Besides the government-sanctioned violence, rebel fighters are launching increasingly deadly attacks on regime targets, and several massive suicide attacks this year suggest al-Qaida or other extremists are joining the fray. Syria severely restricts the media in the country, making it difficult to gain a credible account of events on the ground.
Still, shabiha gunmen have a long history in Syria, dating back to Assad's father and predecessor, Hafez, who ruled Syria from 1971 until his death in 2000.
Under Hafez Assad, shabiha gangs were armed through the military units commanded by Hafez's brother, Rifaat, and their criminal exploits included racketeering, theft, blackmail and armed robbery. They also operated extensive smuggling rings, ferrying weapons, drugs, electronics and cigarettes to neighboring states.
Mousab Alhamadee, an activist based in the central province of Hama, said the shabiha appear to be operating increasingly as rogue elements, without direct orders from on high.
"The shabiha are more and more out of government control," he said, and said the Houla massacre appeared to be a case in point.
"This massacre embarrassed the regime a lot," he said. "The regime tries to avoid such crimes because of pressures from the international community and Russia."
Still, the links with the regime remain strong. Alhamadee said he notices shabiha in areas that are newly taken over by government troops.
"They move behind the troops, and their jobs is to rob and loot," he said.
The presence of shabiha is exacerbating dangerous sectarian tensions in Syria, where Alawite dominance has bred smoldering resentment.
Sunnis make up most of Syria's 22 million people, as well as the backbone of the opposition. The opposition insists the movement is entirely secular, but some reports suggest religious tensions are boiling over.
Activists say as many as 13,000 people have been killed in Bashar Assad's crackdown on the uprising, which began in March 2011, and the death toll rises every day.
Syria is not the first country to use gunmen to carry out its dirty work. During Egypt's revolution, pro-regime gangs enjoyed at least tacit approval from the state, or elements of it, disbanding as quickly as they formed.
Iran's powerful Revolutionary Guard is backed by a vast volunteer paramilitary force known as the Basij, which acts as pro-government monitors in nearly every neighborhood and can be unleashed as street-level muscle for the ruling system.
Basij members were called out in 2009 to help crush protests after the disputed re-election of Iranian President Mahmoud Ahmadinejad, but were mostly armed with clubs and batons to disperse and intimidate crowds. Some international rights groups, however, accused Basij gunmen of several killings during the unrest.
But shabiha fighters have a tighter link to the Syrian regime than patriotism or protecting the privileges they enjoy under Assad's rule.
Because most shabiha fighters are Alawites, their loyalty to the regime is assured _ in part out of fear they will be persecuted if the Sunni majority gains the upper hand.
An offshoot of Shiite Islam, the Alawite sect represents little more than 10 percent of the population in Syria. Assad has long pushed a strictly secular identity in Syria but now is relying heavily on his Alawite power base to crush the uprising.
Some Syrians blame the regime for the shabiha violence, even if the gunmen never received direct orders from Damascus.
"We do not differentiate between the shabiha and the regime's security forces," Ahmed al-Qassem, an activist and Houla resident, told The Associated Press. "Saying that the shabiha were responsible for the massacre in Houla does not absolve the government forces from responsibility. They are one and the same."
AP writers Bassem Mroue and Zeina Karam contributed to this report.