Local officials said about 750 people were arrested. The country's two main NGOs said several people were killed and dozens were injured.
On Tuesday, Venezuela's defense minister described the protests as a “coup.”
Surrounded by armed soldiers, General Vladimir Padrino read out a statement saying President Nicolás Maduro had the military's “absolute loyalty and unconditional support.”
Venezuela's attorney general, a close ally of President Maduro, said one soldier was killed in anti-government protests.
Opposition leader Maria Corina Machado insisted the protests must be peaceful.
“We must proceed peacefully. We must not fall into the provocations that the government has imposed on us. They want to pit Venezuelans against each other,” she said.
“Our candidate won 70% of the vote. We united the country, and Venezuelans who once trusted Maduro are with us today.”
One anti-government protester, who did not want to be named and feared a backlash from security forces, told the BBC he had seen evidence of election fraud.
“We are convinced that the election was stolen. I worked in the polling booth. The government refuses to acknowledge it, they stopped counting all votes in the middle of the night. They don’t want the world to know that they lost,” they said.
They said Venezuelans, known as Chavistas, who supported former leader Hugo Chavez, were now withdrawing their support for President Maduro.
“This is a very peaceful protest. This is an upper-class area of Caracas. What we saw yesterday was very violent. I believe that people who were Chavistas before are no longer Chavistas,” they said.
“I think people are looking for change. It's probably going to be violent.”
