At night, the gunmen cover their faces with ski masks and set up checkpoints, brandishing pistols and ordering residents to identify themselves as they enter the neighborhood.

Here in the 23 de Enero slum, several gangs that pledge allegiance to Venezuelan President Hugo Chavez are effectively the law, ruling over fiefdoms where police seldom venture. Chavez has occasionally criticized the groups, but the authorities have largely left them alone, stoking accusations by critics that the government is tolerating an armed wing that could prove dangerous in a critical election year in Venezuela.

One of the biggest gangs calls itself “La Piedrita,” or “Little Rock.” In its neighborhood turf, murals are painted with slogans such as “For the defense of the revolution, vote for Chavez. La Piedrita.” Murals there depict Jesus and the Virgin Mary holding assault rifles.

“These illegally armed groups could at some point use those weapons to commit crimes or to destabilize any government,” said Luis Izquiel, who leads a security committee for the opposition.