Venezuelan opposition leader Juan Guaido called for a massive May Day protest to increase the pressure on President Nicolas Maduro after a day of violent clashes on the streets of the capital.

Guaido said Wednesday's rally would be "the biggest in the history of Venezuela" as he presses his attempt to unseat the president.

"Across all of Venezuela, we will be in the streets," said the National Assembly leader, recognized as interim president by more than 50 countries, as he repeated his call for the armed forces to join "Operation Freedom" to overthrow the socialist leader.

Maduro however remained defiant after Guaido's call earlier Tuesday for the military to rise up appeared to have largely failed.

Following a day of clashes between demonstrators and police on the streets of Caracas, Maduro Tuesday evening said he had defeated an attempted coup.

Maduro, who is also due to lead a May Day rally in Caracas, declared victory over the uprising -- congratulating the armed forces for having "defeated this small group that intended to spread violence through putschist skirmishes."

"This will not go unpunished," Maduro said in an address broadcast on television and radio.

"(Prosecutors) will launch criminal prosecutions for the serious crimes that have been committed against the constitution, the rule of law and the right to peace."

Tensions in Venezuela have been ratcheted up to a critical level this year, after Guaido announced on January 23 that he was the acting president under the constitution. He said Maduro had been fraudulently re-elected last year.

- 'No turning back' -

Guaido had rallied his supporters with a video message early Tuesday that showed him -- for the first time -- with armed troops who he said had heeded months of urging to join his campaign to oust Maduro.

He claimed the move was the "beginning of the end" of Maduro's regime, and there was "no turning back."

"We showed there are soldiers willing to defend the constitution, and there are many more," Guaido said in the video message.

The 35-year-old opposition leader was filmed outside the La Carlota air base, where he asked the armed forces inside to join him.

Guaido had been immediately backed by the United States, where President Donald Trump said in a tweet Tuesday that Washington was standing behind the Venezuelan people and their "freedom."

Thousands of opposition supporters flocked onto a highway near the air base, many waving Venezuelan flags, but they were met with gunfire and tear-gas fired by soldiers at the compound's perimeter.

Soldiers backing Guaido wore blue armbands to demonstrate their allegiance to the opposition leader but there appeared to be few of them.

Riots also erupted in several other cities across the country, with dozens injured and one death reported, according to human rights groups.

Brazil said a number of Venezuelan troops had sought asylum at its Caracas embassy. Brazilian media put that number at 25.

But Maduro had called on his forces to show "nerves of steel" and troops in riot gear, backed by armored vehicles and water tankers, lined up against the demonstrators.

Hours after the revolt by military officers appeared to be fizzling out, US Secretary of State Mike Pompeo told CNN he believed Maduro was ready to flee to ally Cuba before he was dissuaded by Russia -- a claim Maduro later refuted as "a joke."

- 'Another sunrise' -

Speaking late Tuesday to business executives in Washington, Pompeo voiced hope that Maduro would still choose exile in the coming days.

"I must say, there will be another sunrise tomorrow. The opportunity for Venezuelan democracy, I am confident, will remain," Pompeo said.

Moscow, Maduro's main backer and creditor alongside China, accused Guaido of "fueling conflict" in the oil-rich country while the Syrian government condemned the "failed coup attempt".

Maduro's leftist Latin American allies Bolivia and Cuba also condemned Guaido.

As UN Secretary General Antonio Guterres appealed to all sides to avoid violence, Venezuela's army chief and defense minister General Vladimir Padrino issued a stark warning of possible "bloodshed" -- adding that he would hold the opposition responsible.

The US, meanwhile, called on the military to protect the people and support "legitimate institutions" including the opposition-controlled National Assembly.

Trump threatened a "full and complete embargo" and tougher sanctions against Cuba if it does not end military support for Venezuela.

Although Trump has repeatedly said "all options" are on the table regarding Venezuela -- including, implicitly, military action -- there has been no noticeable US military mobilization.

Instead, Washington has upped the economic pressure, through sanctions aimed at Maduro's regime and by cutting sales of Venezuelan oil -- its main revenue earner.