Venezuelan President Nicolas Maduro has accused protesters of setting fire to a government supporter.
He said "Nazi-fascist" elements are taking root inside the opposition's ranks and contributing to a dangerous spiral of violence in the two-month anti-government protest movement.
Mr Maduro said on Sunday that 21-year-old Orlando Zaragoza suffered burns to almost all his body when he was doused with petrol and set on fire at a protest in Caracas a day earlier.
Videos circulating on social media show a man covered in flames fleeing a small mob.
Mr Maduro said he was being treated.
It is not clear what triggered the attack, which is under investigation, although some eyewitnesses told local media that Mr Zaragoza was caught robbing demonstrators who had gathered by the tens of thousands to protest against Mr Maduro's rule.
"In Venezuela there's rising a counter-revolution of Nazi-fascist influence that has infected the emotions and thinking of thousands of compatriots, who believe they have the right to pursue others for the simple crime of being Venezuelan or Chavista or revolutionary," Mr Maduro said in his weekly TV programme.
"This is terrorism."
Also on Saturday, a 23-year-old was killed with gunshot wounds to the chest during a protest in western Venezuela.
His death brought to at least 48 the number of people killed since anti-government unrest began two months ago.
The street clashes engulfing Venezuela appear to be growing increasingly violent, with both security forces and youth protesters looking more unruly.
Residents of Caracas awoke to several smouldering barricades made of trash and torn-down street signs on Monday.
Meanwhile access to the capital's centre was blocked at several points by heavily armed security forces looking to prevent a planned march to the Health Ministry to demand Mr Maduro open a so-called humanitarian corridor for the delivery of medicine and food aid.
On the outskirts of Caracas, where reports of night-time protests and looting have become more frequent, the situation was even more tense:
Young males with their faces covered or wearing gas masks put down barbed wire at roadblocks every few blocks and menacingly asked bystanders for contributions to their "Resistance" movement.
Opposition leaders are urging restraint from their followers, but say security forces and pro-government militias - not the protesters - are behind the vast number of deadly attacks.