Supporters of Venezuela’s leader, Nicolás Maduro, and his US-backed challenger, Juan Guaidó, returned to the streets on Saturday amid fears the political crisis could be entering a turbulent new phase.

After a strained 48 hours for Venezuela, in which almost the entire country was affected by a blackout, thousands of demonstrators turned out to champion their respective leaders, both of whom claim the presidency.

“I’m here to support President Maduro … he is the constitutional president of our Bolivarian Republic of Venezuela,” said María Reyes, a 52-year-old woman who was among the crowds at a pro-Maduro rally in central Caracas. She said she was there to defend Hugo Chávez’s political heir and denounce “the imposter Guaidó” as a threat to peace.

Experts blame the massive power cut on poor maintenance, incompetence and corruption. But Maduro and his backers claim it was part of a US plot to destroy Chávez’s leftist Bolivarian revolution and force him from power.

“We condemn this cowardly terrorist attack,” tweeted Bolivia’s president, Evo Morales, one of Maduro’s few remaining regional allies.

Reyes said she believed that version, but was also willing to countenance opposition claims that the blackout was caused by government failings. “Perhaps it was a lack of maintenance. We aren’t ruling any hypothesis out,” she said.

Oskar Oramas, a 24-year-old student activist for Maduro’s ruling Socialist party, said he was protesting the “escalation of persecution” against his government by the US. “I have come to take a stand against the United States because they have made it clear they are our enemies … We will defeat them because we are experts in peace,” he added.

“They want to turn us into another Syria and we will not allow this to happen,” one activist shouted from a red sound truck bearing the slogan: “Here you don’t speak badly of Chávez!”

In cities across Venezuela, members of the opposition poured on to the streets to demand political change amid fears that Maduro’s security forces would seek to put down anti-government protests with force.

“They have destroyed a whole country,” demonstrator Jorge Lulo, a psychologist, told the Efecto Cocuyo website as he marched in Caracas carrying his country’s red, yellow and blue tricolor. “We are fighting to escape from tyranny.”

Guaidó, who most western governments have recognised as Venezuela’s legitimate president, told supporters at the rally: “Right now we are [protesting] in more than 50 cities around the country in order to bring an end to the darkness, the hunger and the misery.”

Speaking through a loudhailer, he urged demonstrators to remain mobilised “until we achieve the freedom of Venezuela” and announced that he would summon a peaceful march on the capital at a yet-to-be announced date.

“Today this [tragedy] has a name and a surname … Nicolás Maduro!”, Guaidó said to loud cheers.

The latest chapter of Venezuela’s long-running political crisis began on 23 January when Guaidó, a young opposition leader, declared himself the legitimate interim president. He was quickly recognised by regional powers including Brazil, Colombia and the US, and anti-government demonstrations ensued, leaving many convinced that Maduro’s fall was imminent.

Those predictions did not come to pass, however, and the opposition challenge had appeared to be losing steam. Last week, however, Guaidó made his return to Venezuela after conducting a tour of South America in violation of a travel ban imposed by Maduro’s government.

Efforts to unseat Maduro may also be re-energised by this week’s power cut, which left hospitals and homes without power, and reinforced opposition to him.

“This is a joke,” complained one disillusioned civil servant who was looking on as the pro-Maduro march passed down Avenida Mexico in Caracas. “We’ve got no electricity and they’re using the generators to stage a march rather than sending them to the hospitals.”

“His government is like a cancer,” added a woman, who asked not to be named for fear of reprisals. “This government is a goner.”

On Saturday, anti-Maduro marches were also reported in cities across the country including Barcelona, Barquisimeto, Coro, La Asunción, Maracaibo and Puerto Ordaz.

The power outage, which continues to blight large swathes of Venezuela, has also sparked fears that the South American country could enter a period of disorder.

“It’s a tinderbox, and Maduro’s survival thus far gives a false sense of stability,” said Benjamin Gedan, the national security council’s Venezuela adviser during the Obama presidency. “A sustained blackout could … spark widespread dissent.”

Geoff Ramsey, a Venezuela expert at the Washington Office on Latin America, said that despite the battle of rhetoric between Maduro and Guaidó, he believed some kind of back-channel talks were taking place that could lead to a peaceful settlement.

“I get the sense things are happening behind the scenes. I am more optimistic than I was, say, a month ago about the prospect of some kind of non-violent, negotiated transition,” Ramsey said.

Addressing his rally on Saturday, Maduro lashed out at his political foes in Venezuela and the US and accused “infiltrated coup-mongers and saboteurs” of attacking the country’s electricity system in a high-tech bid to topple him.

“We are at war,” Maduro said. “We have been at war for 20 years.”