It was quiet in the dank basement in northwest Caracas, where dozens of young men and women sat on the floor and assembled their weapons. They poured asphalt, gasoline and paint into beer and pop bottles, tying knots in strips of fabric to fashion wicks.

Molotov cocktails are cheap and easy to make. Whether they're doing the job is at the core of a bitter debate in Venezuela. After months of relentless demonstrations against President Nicolas Maduro, many militants are frustrated. The crew in the basement talked about it in hushed voices — they didn't want anyone in the middle-class neighborhood to find them out. It was clear, though, that many had reached their limit.

The security forces they're up against, the riot-helmeted troops shooting tear-gas canisters and water cannon and bullets? "They all deserve to die," one of the bomb makers said flatly, dripping petrol into a jar.

The call to arms coming from some in the resistance may be the initial stirrings of the kind of urban guerrilla movement the country hasn't seen in half a century. It's too early to tell if they'll actually follow through on their threats, but the bold talk is a troubling sign for mainstream opposition leaders who have issued instructions — pleas, recently — for peaceful rallies and marches.

Those calls increasingly fall on deaf ears. Masked activists hurl their homemade bombs, rocks, jars filled with feces, anything they can get their hands on. They've stormed office buildings, shattered store windows and blocked roads.

"We do not know exactly how to control them, and we are scared that they can get out of hand and damage our fight," said National Assembly Deputy Angel Alvarado, a longtime foe of Maduro and his predecessor and mentor, Hugo Chavez. "These radical boys are a danger."

A young man on a street corner in Caracas, his face covered by a white bandanna, dismissed that as the obsolete opinion of the old guard. His view? "We are tired of being killed," he said as crowds surged around him, agitators suited up in hardhats and bicycle helmets and swimming goggles and gas masks, some carrying shields made of old skateboards as protection.

"We are willing to go out with guns, to face them as equals," he said, declining to give his name, describing himself only as an anti-Maduro fighter from a middle-class family. "The protest must evolve."

More than 100 people have died since daily demonstrations began in April. Hundreds of thousands sometimes pour into the streets in Caracas and other cities, railing against what they consider an authoritarian regime. Disgust with Maduro has swept into every class, uniting rich and poor as his leftist government plunged Venezuela into an unprecedented economic collapse. In a country with the world's largest crude-oil reserves, there are critical shortages of food, medicine and cash.

The opposition momentum has been building since Maduro unveiled plans to rewrite the country's constitution, calling a special National Constituent Assembly election for July 30. The president said in a statement that those who want to disrupt the vote or not participate are "hurting the right for peace, because what we are deciding here next week is between peace or war, violence or the constituent assembly."

Outraged Venezuelans brought the capital to a virtual standstill last week with marches. More than 7.5 million cast votes in an unofficial plebiscite against the president and his assembly plan, denounced as a ploy to consolidate power. The U.S. is weighing sanctions. Maduro in a television appearance on Sunday was unyielding. "The imperial right wing believes it can give orders to Venezuela," he said. "The only ones who give orders here are the people."

Maduro's defiant intransigence in the face of widespread opposition is proof, according to the radicals, that they need to move on from Molotov cocktails, from torching the occasional government vehicle or setting trash bins on fire.

The view from the more conservative in the anti-Maduro coalition is that they have already gone too far. "There is an element of anarchy," said Ramon Muchacho, mayor of the Chacao district of Caracas, which is ground zero for protests in the capital. "And there are groups of people who take advantage of the situation.''

Like the looters who wear masks when they ransack shops. They're criminals exploiting the chaos on the streets, said Fernando Fernandez, who owns a liquor store in Caracas. A dozen of them broke in on a recent Friday and made away with a trove of booze. "This is the first time anything like this has ever happened," he said. "They weren't the resistance, they were thugs."

That's one of the many dangers cited in arguments against stepping up the fury in the oust-Maduro campaign: that violence condoned in the name of righteous political opposition is difficult to direct.

It may also be just what pro-Maduro forces want, "so they can justify more attacks and deaths," said Rafaella Requesens, 25, a leader in the Venezuelan Student Movement. "I call on all these kids who want to escalate the protest and turn it into a violent one to think twice. We cannot play their game."

The young man in the white bandanna in Caracas said the time for restraint has passed: The fatalities are mounting, averaging one a day since the protests began, and Maduro is still president.

"If they shoot us with firearms? We have to shoot them, too."

Bloomberg's Andrew Rosati contributed.