A major conflict erupted Tuesday in Venezuela’s capital, with opponents of the government determined to topple the country’s strongman president, Nicolás Maduro.

The opposition leader, Juan Guaidó, appeared at an air base in Caracas, urging the military to join the uprising. Guaidó declared himself interim president earlier this year.

Throngs of protesters took to the streets and there were clashes between Guaidó’s supporters, including some troops, and Venezuelan national police, who fired tear gas. The number of casualties, if any, remains unclear but cameras caught military vehicles driving through pro-Guaidó protesters. **Warning – This video contains graphic images.

In a video posted on social media, Guaidó said he has support from “brave soldiers, brave patriots, brave men attached to the Constitution.” He declared that this is the start of the “final phase” of his campaign to bring down Maduro.

Despite Guaidó’s appeal for help from the armed forces, he and his top associates deny the uprising is a classic military coup.

“While Mr. Guaidó has exhorted the Venezuela military to join his side,” reports the New York Times, “it was a new step for him to make the declaration with men in uniform by his side. Still, it was unclear how much of the military supports him.”

CBS News says there appeared to be “about two dozen troops” behind Guaidó as he spoke, along with “a couple of armored vehicles.”

Following his dawn appearance at the air base, CNN says, Guaido made his way to Plaza Altamira, the center of the city’s opposition heartland, where he told supporters that “today it’s clear to us that the armed forces are with the Venezuelan people, who are not with a dictator.”

But Maduro “insisted in a Twitter post that the military was on his side,” says the Times, “saying commanders had assured him of ‘their total loyalty to the people, to the Constitution and to the fatherland.’”

The White House said Tuesday it is watching to see if the uprising succeeds, but hopes it will bring democracy to Venezuela.

“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,” says CBS. Bolton declared that “The United States stands with the people of Venezuela.” He also said all options are on the table.

But what if the uprising sputters or fails? One U.S. Senator took it a step farther.

Under Maduro’s leadership and U.S. sanctions, the once-vibrant Venezuelan economy has virtually collapsed, fueling the opposition to his regime.

“Battered by mismanagement, American sanctions and corruption, the Venezuelan economy has been in steep decline since 2014,” says the Times. “Millions of people have emigrated, and the roughly 30 million who remain are plagued by hyperinflation and shortages of medicines, food, electricity and jobs.

The Trump administration recognized Guaidó as the legitimate leader of the country following Maduro’s re-election victory last year — “an election widely deemed flawed and undemocratic,” says CBS. Dozens of other nations also support Guaidó.

Russia is Maduro’s main foreign backer. A Kremlin spokesman said Russian President Vladimir Putin is closely following developments in Venezuela.