Venezuelan opposition leader Maria Corina Machado has spoken at a major rally in the capital Caracas, despite calls from the government for her arrest.
Ms Machado went into hiding earlier this week after accusing President Nicolás Maduro of cheating opposition candidate Edmundo Gonzalez out of a clear victory in the presidential election.
The president, in turn, accused Ms. Machado of inciting violence and said she and Mr. Gonzalez faced decades in prison.
The electoral commission – controlled by Mr Maduro’s allies – has confirmed he won with 52% of the vote last Sunday, but independent observers say this lacks transparency.
The commission has not yet released full results. The opposition said its vote count showed it had won by a large margin. Pre-election polls showed a clear victory for the challenger.
On Saturday, Ms Machado addressed thousands of her supporters in Caracas from a truck carrying a banner reading “Venezuela has won”.
“We have never been stronger than we are today,” she told the crowd, adding that “this regime has never been weaker… It has lost all legitimacy.”
The opposition leader, who was prevented from running in the election, spent days in hiding.
Earlier this week, Ms. Machado wrote in The Wall Street Journal that she and many other opposition leaders were “fearing for our lives.”
She was greeted with cheers of “freedom, freedom” and was accompanied by several other opposition leaders – but not Mr Gonzales.
In a separate video message, he called on supporters to “respond to the regime’s attacks with hope, harmony and peace”.
Security forces in Venezuela have spent days trying to contain mass protests. At least 11 people have been killed in clashes with police.
More than 1,000 opposition protesters were arrested.
The government is under increasing international pressure, with US Secretary of State Antony Blinken saying on Friday there was “clear evidence” that Mr Gonzalez won the election.
His intervention comes as the presidents of Brazil, Mexico and Colombia have all called on Venezuela to release detailed election results.
Other regional governments, including Argentina, Costa Rica, Panama and Uruguay, have expressed concern about the vote.
But Mr Maduro has the backing of allies in Russia, China and Cuba.
He has asked Venezuela’s supreme court to audit the vote count to confirm the results, giving him another six-year term in power.
The opposition says the court is in the hands of government loyalists who will delay the release of the figures. Mr Gonzalez boycotted the hearing on Friday.
