A woman was shot dead and dozens injured in the Venezuelan capital Caracas on Wednesday, in clashes between opposition supporters and pro-government forces.
Tear gas and water cannon were fired by the military amid rival demonstrations.
Opposition leader Juan Guaidó called for those responsible for the death of a 27-year-old woman to be found.
Meanwhile, Mr Guaidó called for a series of strikes to force President Nicolás Maduro to relinquish power.
He urged public employees to act on Thursday, saying the stoppages would lead to a general strike.
Mr Guaidó in January declared himself Venezuela’s interim leader, and he has been recognised by more than 50 countries including the US, UK and most Latin America nations.
But Mr Maduro – who is backed by Russia, China and the leaders of Venezuela’s military – has refused to cede power.
The president dismissed suggestions he had been ready to flee the country and accused the US of directing an attempted coup. Those involved would be punished, he said.
In a series of tweets (in Spanish), Mr Guaidó said the final phase of “Operation Liberty” had begun and it was the turn of public workers to join in.
He urged protesters to stay on the streets until Mr Maduro’s government would be finally forced to resign.
Mr Guaidó has been courting the public sector for weeks – but winning their support will be difficult, the BBC’s Americas editor Candace Piette says.
For years, state employees have been told that if they did not turn up at government rallies they would lose their jobs.
So if the opposition leader does win them over, it will be a huge victory against President Maduro, our editor says.
Tensions are rising between the US and Russia over the crisis.
US Secretary of State Mike Pompeo said the US may take military action to resolve the crisis, and accused Russia and Cuba of destabilising the country through their support for Mr Maduro.
The US also reiterated its support for Mr Guaidó.
Russian Foreign Minister Sergei Lavrov told Mr Pompeo that America’s influence over Venezuela was destructive and a violation of international law.
UN Secretary General António Guterres has appealed for both sides in Venezuela to avoid violence, while the EU has called for “utmost restraint to avoid the loss of lives and an escalation in tensions”