CARACAS, Venezuela >> Venezuelan opposition leader Juan Guaidó took to the streets with a small contingent of heavily armed troops early today in a bold and risky attempt to lead a military uprising and oust socialist leader Nicolas Maduro.

The early-morning rebellion seems to have only limited military support. But it was by far the most-serious challenge yet to Maduro’s rule since Guaidó, with the backing of the U.S., declared himself the country’s interim president in January in rejection of a government he accused of “usurping” power.

The dramatic events began early today when Guaidó, flanked by a few dozen national guardsmen and some armored vehicles, released a three-minute video filmed near a Caracas air base in which he called on civilians and others in the armed forces to join a final push to topple Maduro.

In a surprise, standing alongside him was Leopoldo Lopez, his political mentor and the nation’s most-prominent opposition activist, who has largely been unseen since he was detained in 2014 for leading anti-government protests. Lopez said he had been released from house arrest by security forces adhering to an order from Guaido.

“I want to tell the Venezuelan people: This is the moment to take to the streets and accompany these patriotic soldiers,” Lopez declared.

As the two allies coordinated actions from vehicles parked on a highway overpass, troops loyal to Maduro sporadically fired tear gas from inside the adjacent Carlota air base. A crowd that quickly swelled to a few thousand scurried for cover, with a smaller group of masked youths reassembling outside the air base’s gates where they lobbed rocks and other heavy objects.

“It’s now or never,” said one of the young rebellious soldiers, his face covered in the blue bandanna worn by the few dozen soldiers who stood alongside Guaidó and Lopez.

Maduro tried to project an image of strength, saying he had spoken to several regional military commanders who reaffirmed their loyalty to his socialist revolution.

“Nerves of steel!,” he said in a message posted on Twitter.

The dramatic events, playing out in the opposition’s stronghold in wealthier neighborhood of eastern Caracas, appeared not to have triggered a broader military revolt.

Defense Minister Vladimir Padrino on Twitter rejected what he called an attempt by a “subversive movement” to generate “panic and terror.”

The ruling socialist party chief, Diosdado Cabello, said most of Caracas was calm and called on government supporters to amass at the presidential palace to defend Maduro from what he said was a U.S.-backed coup attempt.

About a dozen government supporters, some of them brandishing firearms, gathered at the presidential palace, answering the call by Cabello to defend Maduro.

“It’s time to defend the revolution with arms,” Valentin Santana, head of a militant group, said in a video posted on social media as he brandished an automatic rifle.

Guaidó said the troops who had taken to the streets were protecting Venezuela’s constitution. He said that in the coming hours he would release a list of top commanders supporting the uprising.

“The armed forces have taken the right decision,” said Guaidó. “With the support of the Venezuelan people and the backing of our constitution they are on the right side of history.”

As events unfolded, governments from around the world expressed a mix of support for Guaidó while reiterating calls to avoid violent confrontation.

U.S. National Security Adviser John Bolton, in a Twitter post directed at defense minister Padrino, said the armed forces “must protect the Constitution and the Venezuelan people.”

Meanwhile, Spain’s caretaker government urged restraint, while the governments of Cuba and Bolivia reiterated their support for Maduro.

“We hope with all of our strength that there is no bloodshed. We support a peaceful democratic process in Venezuela. We support the immediate holding of an election for a new president,” Spanish government spokeswoman Isabel Celaá said.