* Opposition leader says he has begun move to oust Maduro
* No sign yet of widespread military support
* Gunshots at Guaido rally outside Caracas air base
* Maduro says he has total loyalty of armed forces
Venezuelan opposition leader Juan Guaido on Tuesday called for a military uprising to oust President Nicolas Maduro and violence broke out at anti-government protests as the country hit a new crisis point after years of political and economic chaos.
Several dozen armed troops accompanying Guaido clashed with soldiers supporting Maduro at a rally outside the La Carlota air base in Caracas, but the incident fizzled out and did not appear to be part of an immediate attempt by the opposition to take power through military force.
Guaido, in a video posted on Twitter earlier on Tuesday, wrote that he had begun the "final phase" of his campaign to topple Maduro, calling on Venezuelans and the armed forces to back him ahead of May Day mass street protests planned for Wednesday.
Protests broke out on Tuesday. A National Guard armored car slammed into anti-Maduro protesters who were throwing stones and hitting the vehicle in Caracas, television images showed.
Defense Minister Vladimir Padrino called the latest instability a "coup movement" but several hours after Guaido's announcement there was no sign of any other anti-Maduro military activity and no immediate reports of casualties.
Guaido later left a rally he was holding with military supporters at the air base. Repeated opposition attempts to force Maduro, a socialist, from power through huge protests and calls on the military to act have so far failed.
Maduro said on Tuesday he had spoken with military leaders and that they had shown him "their total loyalty."
"Nerves of steel!" Maduro wrote on Twitter. "I call for maximum popular mobilization to assure the victory of peace. We will win!"
The move was Guaido’s boldest effort yet to persuade the military to rise up against Maduro. If it fails, it could be seen as evidence that he lacks the support he says he has. It might also encourage the authorities, who have already stripped him of parliamentary immunity and opened multiple investigations into him, to arrest him.
The United States is among some 50 countries that recognize Guaido as Venezuela's president, and has imposed sanctions to try to dislodge Maduro, who they say won re-election last year through fraud.
"Whatever happens now, we won't let ourselves be stopped. Our process is moving on step by step, in accordance with our constitution. We continue to stand for nonviolence," Guaido told German international broadcaster Deutsche Welle in an interview released on Tuesday.
Oil prices topped $73, partly driven higher by the uncertainty in Venezuela, an OPEC member whose oil exports have been hit by U.S. sanctions and an economic crisis.
Guaido's efforts appeared aimed at building momentum toward the May Day mass street protests and making them a turning point in his push to oust Maduro.
Guaido has said Wednesday's protests will be "the largest march in Venezuela's history" and part of what he calls the "definitive phase" of his effort to take office in order to call fresh elections.
Venezuela is mired in a deep economic crisis despite its vast oil reserves. Shortages of food and medicine have prompted more than 3 million Venezuelans to emigrate in recent years.
The slump has worsened this year with large areas of territory left in the dark for days at a time by power outages, cutting off water supplies and cellphone service.
Guaido, the leader of Venezuela's opposition-controlled National Assembly, in January invoked the constitution to assume an interim presidency, arguing that Maduro's re-election in 2018 was illegitimate.
U.S. President Donald Trump "has been briefed and is monitoring the ongoing situation," White House spokeswoman Sarah Sanders said on Tuesday. The White House declined to comment on whether the administration had been consulted or had advance knowledge of what Guaido was planning.
U.S. national security adviser John Bolton appeared to back Guaido's actions on Tuesday. "The FANB must protect the Constitution and the Venezuelan people. It should stand by the National Assembly and the legitimate institutions against the usurpation of democracy," Bolton tweeted, referring to the FANB armed forces.
Conservative Republicans in Washington welcomed the reports from Venezuela. Senator Marco Rubio, a hard-liner on Venezuela, urged Venezuelans to take to the streets: "Do not allow this moment to slip away. It may not come again," he wrote on Twitter.
Brazil's right-wing President Jair Bolsonaro expressed his nation's solidarity for the people of Venezuela, who he said were "enslaved by a dictator."
Venezuelan Information Minister Jorge Rodriguez on Tuesday tweeted that the government was confronting a small group of "military traitors" seeking to promote a coup.
Guaido, in the video on his Twitter account, was accompanied by men in military uniform and opposition politician Leopoldo Lopez, who had been placed under house arrest.
Maduro, for his part, has appeared to retain control of state institutions and the loyalty of senior military officers and has foreign allies such as Russia and Cuba.
Russia's foreign ministry on Tuesday accused the Venezuelan opposition of resorting to violence in what it said was a brazen attempt to draw the country's armed forces into clashes.
Maduro has called Guaido a U.S-backed puppet who seeks to oust him in a coup. The government has arrested his top aide, stripped Guaido of his parliamentary immunity and opened multiple probes. It has also barred him from leaving the country, a ban Guaido openly violated earlier this year.
Last week, Guaido said his congressional ally - opposition lawmaker Gilber Caro - had been detained, and that 11 members of his team had been summoned to appear before the Sebin intelligence agency.
Lopez, seen with Guaido, appeared to have left his home for the first time since being placed under house arrest in 2017, after three years in jail.
"I have been freed by soldiers on the side of the constitution and President Guaido," he tweeted. All of us have to mobilize. It's time to win our freedom."
A soldier in the group with Guaido, who identified himself just as Rivas, denied government accusations that they had been tricked into backing Guaido.
"We're all afraid," he told Reuters, "but we had to do it".