Five protesters were shot and injured — including one as young as 15 — as thousands have spilled onto the streets in Venezuela since Tuesday.
Some of the protests are calling for government reform, while others rallied to support the 10-month-old term of President Nicolas Maduro.
“They were attacked by the 'colectivos' [militant community groups] while exercising their right to peaceful protest,” opposition activist Tamara Suju told Reuters.
The attacks happened late Tuesday in the city of Merida.
Thousands more descended onto the streets of the capital, Caracas, on Wednesday to mark Youth Day.
The annual celebration remembers students who participated in a 19th century independence battle against colonial authorities.
Maduro — who won the presidency after his mentor Hugo Chavez died last March — promised swift retaliation.
“They want to bring down the legitimate government that I lead. They are not going to achieve it,” Maduro said in a speech late on Tuesday, according to Reuters.
“They are going to damage Venezuela. ... They should correct their behavior in time. If they don’t ... I will apply the law and the constitution with absolute severity against ‘coupsters,’ destabilizers and violent sectors, whoever they are.”
Venezuela, despite its oil wealth, is combatting 50 percent annual inflation and a dwindling supply of consumer products. Everything from food to toilet paper to newsprint are in high demand.
Opponents charge the government with debilitating currency and price controls.
“We will not kneel,” David Smolansky, mayor of a community near Caracas, shouted during protests, Agence France-Presse said. “They have taken our students prisoner. We want them released.”