Venezuelan President Nicolás Maduro tweeted photos of himself with the military in a show of defiance against opposition leader Juan Guaidó.
Maduro called the march a "clear demonstration of the moral strength and integrity of our glorious armed forces".
It comes as the Venezuelan Observatory of Social Conflict says at least three people were killed and 130 injured as pro- and anti-government protesters clashed over the past two days.
Jurubith Rausseo, 27, and Yoifre Hernandez Vasquez, 14, both died in Altamira, while Yosner Graterol, 16, was shot dead in Victoria.
The NGO estimates that at least 55 protesters have died so far in 2019.
Venezuelan opposition leader Juan Guaidó called on Wednesday for a general strike and more demonstrations to force President Nicolás Maduro from power.
In a series of tweets he appealed for a sustained protest as part of “Operation Liberty”, after thousands came onto the streets.
“This is a regime that has lost control. The more we are in the streets, the closer we are,” Guaidó said.
One opposition-controlled district of Caracas saw fresh clashes between demonstrators and security forces. Several dozen people were reportedly injured.
Tear gas was fired at dozens of protesters who threw stones and improvised incendiary devices at security forces close to the military base of La Carlota, where Guaidó claimed on Tuesday to have the support of a group of soldiers.
The opposition leader also expressed his sympathy for two young people reportedly killed during anti-Maduro protests, blaming the regime for their deaths.
Maduro had claimed success in a TV address to the nation and said his rival had failed to turn the military against him, later tweeting several photos of the armed forces marching on Thursday.
In front of thousands of supporters celebrating International Workers’ Day outside the presidential palace – which he later highlighted on Twitter – he said he would have “no hesitation” in putting behind bars “a handful of traitors” he held responsible for fomenting opposition.
The president rejected claims that he had been ready to flee the country, and accused the United States of trying to oust him. Maduro claimed that an attempted coup d’état had been "directed from the White House” and called for an investigation into “illegal actions orchestrated from Washington”, the state-backed TV channel Telesur reported.
The US asserted on Tuesday that the embattled Venezuelan leader was preparing to go to Cuba, but was talked out of it by Russia.
President Donald Trump said the US was doing everything short of “the ultimate” to help resolve the Venezuelan crisis. “We have a lot of options open,” he told Fox News, refusing to be drawn further other than to say some of them were “pretty tough”.
He described the situation as “an incredible mess”, saying that people were starving due to a lack of food in what was one of the wealthiest countries in the world.
US Secretary of State Mike Pompeo has said the US could take military action, and accused Russia and Cuba of destabilising Venezuela by supporting Maduro.
Spain has said that Leopoldo López, an opposition leader who spent years under house arrest and appeared alongside Guaidó on Tuesday, had sought refuge with his family in the Spanish embassy.
The United Nations Secretary General António Guterres has appealed for calm, and the European Union issued a call for “utmost restraint”.
Since January Venezuela has been confronted with the most serious crisis in its history, with economic and monetary collapse bringing a humanitarian emergency. Nearly three million people are estimated by the UN to have left the country since 2015.