About 3,000 opponents dressed in white and carrying red, blue and yellow Venezuelan flags gathered in an affluent area of the capital, fanning out into nearby streets, just days after demonstrations left three people dead.
The protesters, mostly students, have spearheaded nearly two weeks of marches against President Nicolas Maduro, angered by rampant crime, rising prices and a lack of essential supplies as basic as toilet paper in a nation that sits on top of the world's largest proven oil reserves.
On Saturday the demonstrators demanded the release of about 100 detained students and other opposition activists, and an end to police repression, but at least one protest ended with police officers firing tear gas.
The depth of the unrest on what is now the 12th day of street protests was underscored by Maduro's decision to address a counter-rally, and by US Secretary of State John Kerry voicing alarm at the reported arrests.
But speaking before thousands of supporters gathered in downtown Caracas, Maduro accused conservative Colombian ex-president Alvaro Uribe, whom he regards as a US ally and foe of Venezuela, of "funding and directing" the "fascist movements" he blames for the unrest.
Maduro's elected socialist government has also taken Colombian news channel NTN24 off the air, saying it was inciting anti-government violence.
Protests have taken place in different cities in Latin America, and on Saturday, dozens of activists, many of them youths, rallied in front of the Venezuelan Embassy in Washington.
They carried banners reading "SOS Venezuela," "We say no to dictatorship" and "Venezuela is not alone." Many wore clothing in the colors of the Venezuelan flag.
A handful of pro-government protesters held banners at the embassy gates that read "We are with the Bolivarian revolution."
Top US diplomat Kerry said in a statement that reports of Venezuela's leaders arresting scores of anti-government protesters would "have a chilling effect on citizens' rights to express their grievances peacefully," and he called for all parties to work together to resolve tensions.