A woman was shot dead and dozens injured in the Venezuelan capital Caracas on Wednesday, in clashes between opposition supporters and pro-government forces.
The military fired tear gas and water cannon amid rival demonstrations.
Opposition leader Juan Guaidó called for those responsible for the death of a 27-year-old woman to be found.
He also urged public employees to go on strike on Thursday, to try to force President Nicolás Maduro to stand down.
In January, Mr Guaidó 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.
As the head of the opposition-controlled National Assembly, he invoked the constitution to assume an interim presidency, arguing that Mr Maduro's re-election last year was illegitimate.
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.
How did the violence unfold?
On Wednesday, both pro- and anti-government supporters held demonstrations in Caracas that were initially peaceful.
There were reports of gunfire in the city, and a local NGO, the Venezuelan Observatory of Social Conflict, said Jurubith Rausseo, 27, had been shot dead during a rally in the opposition stronghold of Altamira.
At least 46 people were injured in clashes between opposition supporters and the security forces.
On Tuesday, Mr Guaidó posted a video showing him with a number of men in military uniform. He said he had the support of "brave soldiers" in Caracas.
He urged Venezuelans to join them in the streets, and appeared alongside another opposition leader, Leopoldo López, who had been under house arrest after being found guilty of inciting violence during protests in 2014.
Spain's government later said that Mr López and his family had sought safety in their embassy, but said the opposition figure has not claimed political asylum.
Supporters on both sides gathered around the city throughout Tuesday, and there were clashes between Mr Guaidó's supporters and armed military vehicles.
How significant is Guaidó's call for strikes?
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.
What international reaction has there been?
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".
Governments who still back Mr Maduro - including Bolivia and Cuba - condemned Mr Guaidó's efforts as an attempted coup.
The Mexican government expressed "concern about a possible increase in violence" while Colombian President Ivan Duque urged the Venezuelan military to stand "on the right side of history" against Mr Maduro.
An emergency meeting of the Lima Group of Latin American countries has been scheduled for Friday.