The groups, called collectives or colectivos in Spanish, originated as pro-government community organizations that have long been a part of the landscape of leftist Venezuelan politics. Civilians with police training, colectivo members are armed by the government, say experts who have studied them.

These groups seem similar to the Nazi era Brown shirts or to the little green men that Russia used in the war with Ukraine.

Colectivos control vast territory across Venezuela, financed in some cases by extortion, black-market food and parts of the drug trade as the government turns a blind eye in exchange for loyalty.

Now they appear to be playing a key role in repressing dissent.

Hundreds of thousands of protesters have taken to the streets of Caracas and other cities demanding elections in Venezuela. Galvanized by a ruinous economy that has left basic foods and medicines scarce — as well as a botched attempt by leftists to dissolve the country's congress last month — they present the largest threat to the country's rulers since a coup that briefly ousted Mr. Maduro's predecessor, Hugo Chávez, in 2002.