Caracas, Venezuela -- Venezuelan opposition leader Juan Guaido has called for a military uprising in what he dubbed the "final phase" of his bid to oust President Nicolas Maduro – or as he named it, "Operation Freedom." Guaido made the call in a video shot at a Caracas military air base, showing him in front of a group of soldiers and accompanied by previously-detained activist Leopoldo Lopez. In the three-minute video shot early Tuesday, Guaido said soldiers who took to the streets would be acting to protect Venezuela's constitution.

"The moment is now," he said, as his political mentor Lopez and several heavily armed soldiers backed by a single armored vehicle looked on.

Lopez had been under house arrest for leading an anti-government push in 2014. He said Tuesday that he was freed by members of the military, and reiterated Guaido's call on all Venezuelans to peacefully take to the streets.

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"Today, brave soldiers, brave patriots, brave men, supporters of the constitution, have answered our call," declared Guaido in the video. He addressed the rest of Venezuela's security services, which have thus far remained loyal to President Nicolas Maduro: "I invite you to take to the streets."

There appeared to be about two dozen troops behind Guaido in the video posted early Tuesday morning, with a couple of armored vehicles behind them.

Soldiers and people react to the sound of gunfire near the Generalisimo Francisco de Miranda Airbase "La Carlota" in Caracas, Venezuela, April 30, 2019. REUTERS

Later Tuesday morning there was tear gas fired as Guaido's heavily armed supporters from the military took positions around the air base, known as La Carlota. Inside the base a larger contingent of troops still loyal to Maduro could be seen taking positions.

His supporters clashed with security forces still loyal to the government, with rocks being hurled at national police. There was no immediate information on casualties amid the melee.

Maduro's military commanders dismissed the "coup attempt" in social media posts and said the Venezuelan army remained loyal to the president.

The Trump administration was one of the first major world powers to recognize Guadio as the legitimate leader of Venezuela, shunning Maduro after a 2018 election widely deemed flawed and undemocratic saw him win another term.

It was unclear how much advance knowledge the Trump administration had of Guaido's plans for Tuesday, but Mr. Trump's National Security Adviser John Bolton was first to tweet his support. He specifically called on Maduro's Minister of Defense Vladimir Padrino and the Venezuelan army (which goes by the acronym FANB) to "stand by the National Assembly and the legitimate institutions against the usurpation of democracy."

U.S. reaction

"The United States stands with the people of Venezuela," Bolton added. Secretary of State Mike Pompeo also heralded Guaido's fresh effort to gain the military's backing -- which, as CBS News correspondent Elizabeth Palmer has reported, is vital to toppling Maduro. Pompeo said the U.S. government "fully supports the Venezuelan people in their quest for freedom and democracy. Democracy cannot be defeated."

President Trump and his cabinet members have repeatedly warned the Maduro regime not to try and arrest or harm Guaido, hinting that such action could draw a more overt response from the U.S. Thus far American actions have remained in the diplomatic realm -- in the form of sanctions and efforts to get aid materials into economically crippled Venezuela against Maduro's wishes.

The White House said it was "watching and waiting" to see how the events in Venezuela unfolded, but hoping the result would be democracy.

To @jguaido, the National Assembly and all the freedom-loving people of Venezuela who are taking to the streets today in #operacionlibertad—Estamos con ustedes! We are with you! America will stand with you until freedom & democracy are restored. Vayan con dios! #FreeVenezuela — Vice President Mike Pence (@VP) April 30, 2019

"We are with you!" Vice President Mike Pence said in a tweet to Guaidó, the National Assembly and "all the freedom-loving people of Venezuela who are taking to the streets today in #operacionlibertad_Estamos con ustedes! We are with you!"

"America will stand with you until freedom & democracy are restored," Pence said.

Not long after Guaido's video appeared online, Padrino, the defense minister, tweeted that the army was steadfast "in support of the National Constitution and the legitimate authorities" of Venezuela, and that commanders at military bases around the country reported no disturbances.

"They are cowards!" Padrino said of Guaido and his supporters. "We will stay firm in defense of the constitutional order and the peace of the Republic, aided as we are by the law, reason and history. Always loyal, never traitors!"

In spite of steady pressure from the U.S., most Latin American nations and Europe, Maduro has clung to power -- thanks in large part to support from Russia.

Jorge Rodriquez, the Maduro regime's information minister, said in a pair of tweets early Tuesday that security services were "currently confronting and deactivating a small group of military traitors" who it accused of attempting to "promote a coup against the constitution and Peace of the Republic."

"We call on the people to stay on high alert, along with the glorious Bolivarian National armed forces, to defeat the coup attempt and preserve the peace. We will win," wrote Rodriquez.

Kremlin spokesman Dmitry Peskov said Russian President Vladimir Putin raised the developments in Venezuela during a scheduled meeting with his Security Council on Tuesday. Peskov said that the meeting "paid significant attention to the news reports about a coup attempt in that country."