Venezuelan riot police fired tear gas at a demonstration in Caracas called by opposition leader Juan Guaidó on Tuesday to demand elections to replace leftist President Nicolás Maduro.
Thousands of protesters started marching from the east of Caracas towards the National Assembly when they were blocked by a police barricade.
As Guaidó attempted to negotiate with police, they fired tear gas at the demonstrators, AFP reporters at the scene said.
"This picket today does not represent Venezuela, this picket represents the dictatorship," Guaidó said, referring to the line of police with riot shields blocking the way.
Most of the marchers left the area, but some with their faces covered, threw stones at the police.
"A stage of sustained struggle begins today," Guaidó said earlier as he addressed the crowd through a megaphone from the back of a truck.
Thousands of protesters had begun the march in east Caracas waving Venezuelan flags and caps in the national colors. Local media reported smaller protests in other cities.
"Today we reconvene in the streets, the place where the citizens are free," said Guaidó in a tweet.
Guaidó, who heads the opposition-controlled National Assembly, launched a movement to oust Maduro last year, claiming he had usurped power in rigged 2018 elections.
After declaring himself acting president, Guaidó quickly secured the backing of more than 50 countries and initially led street protests drawing tens of thousands of people.
But Maduro weathered the protests and Guaidó's popularity has waned.
He recently returned from a high-profile tour to drum up international support, meeting US President Donald Trump, British Prime Minister Boris Johnson and French President Emmanuel Macron.
Guaidó blames Maduro for a crippling, five-year-long economic crisis that has mired the once rich oil-producing country in deepening poverty and soaring inflation.
Plunging oil prices in world markets Tuesday are the latest shock to the economy, which is almost entirely dependent on revenues from its declining, sanctions-battered oil industry.
"It's 30 years since prices fell like this, it's a tragedy," said Guaidó in reference to Monday's plunge that took almost one-third off the price of oil.
"They've been destroying the Venezuelan oil industry for years. They've destroyed two-thirds of the production capacity ... they've destroyed the debt capacity."