The opposition leader battling to bring the curtains down on Nicolás Maduro’s authoritarian regime has urged the Venezuelan strongman to accept that his exit from power is inevitable. The call came as thousands of protesters hit the streets to repudiate Maduro’s disputed claim to have won a third term in power. Venezuela’s incumbent president was officially proclaimed the victor of Sunday’s election by the government-controlled electoral authority on Monday morning. Maduro called his supposed victory “irreversible” despite widespread international doubts over the veracity of his claim to have won. But speaking to the Guardian, María Corina Machado, the charismatic conservative who is the driving force behind Maduro’s opponent in Sunday’s election, urged the president to come to terms with the end of his 11-year rule during which Venezuela fell into a devastating economic and humanitarian crisis that has forced millions to flee abroad. “He should understand that he was defeated,” she said of Maduro, who was democratically elected after the 2013 death of his mentor, president Hugo Chávez, but has since taken Venezuelan in an increasingly repressive and anti-democratic direction. Machado rejected Maduro’s earlier claim that his re-election was “irreversible”. “I would say his departure is irreversible,” she said. Minutes earlier, Machado and Edmundo González, a former diplomat who ran for the presidency in her place after she was banned, claimed their campaign now had hard evidence that González had secured a landslide victory in Sunday’s vote. Maduro has claimed he beat González, with more than 5.1m votes to his rival’s 4.4m. But Machado, who some call Venezuela’s “iron lady”, insisted her candidate had in fact prevailed with more than 6.2m votes compared to Maduro’s 2.7m. “Edmundo González is the president-elect,” she declared to ecstatic cheers from hundreds of supporters who had packed the street outside their hillside campaign HQ beneath Caracas’s towering El Ávila mountain. As Machado addressed the throng, thousands of dissenters remained on the streets of Caracas and other cities after a day of demonstrations that saw several violent clashes with security forces and pro-Maduro paramilitaries. Remarkably, many of those protesters came from sprawling hillside slums long considered bastions of the chavismo movement that has governed Venezuela for the last 25 years. As Rafael Cantillo marched through Caracas alongside hundreds of fellow residents of one such community, he shook with rage. “Maduro stole these elections … it’s a swindle – everyone knows it,” fumed the 45-year-old who hails from a vast working-class enclave called Petare. Nearby, another community leader from Petare, ️Katiuska Camargo, claimed Maduro had suffered a conclusive defeat in such communities where residents were tired of the deprivation his administration had overseen. “This man did not win. He did not!” she said as the crowd swelled. As the Petare protesters strode west towards the city centre and the presidential palace, they chanted: “Petare is here. And Edmundo is presidente!” Throughout the day social media filled with reports of opposition marches originating in poor communities across town and clashes with security forces and pro-Maduro motorbike gangs known as colectivos who were filmed shooting into the air. “What is happening isn’t just fraud, it is a coup d’état,” said Jesús Herrera, a 37-year-old cook, as he joined one march. Herrera said the people who had taken to the streets were “moved by [Maduro’s] lie”. “It’s such an obvious lie,” he said of the president’s claim to have won re-election when polls had given his rival a major lead. “Everyone thinks the same thing.” There were also protests in other parts of Venezuela, with at least three statues of Hugo Chávez torn down during the day. Many compared those scenes to the dramatic images of a statue of Saddam Hussein being toppled in downtown Baghdad during the Iraq war. In Portuguesa state, protesters were filmed vandalizing a propaganda billboard featuring a photograph of Maduro and a slogan promising “More changes and transformation”. On Monday night there were also reports that protesters had stormed the Maiquetía international airport on the coast just north of Caracas. At least one incoming flight was delayed. Maduro’s allies, who blame Venezuela’s economic woes on US sanctions, called its own protests for Tuesday afternoon in an attempt to show popular support likely to further inflame tensions on the streets of Caracas. In a televised address, Maduro claimed groups of “delinquents” had invaded the regional offices of the electoral authority in the city of Coro. The president said such actions were part of “a violent counter-revolution” being waged by criminal and fascist far-right extremists. “The law must be respected,” Maduro declared, claiming such activities were designed to spark “an escalation of violence” that would ultimately lead to the opposition’s “golden dream – seizing power”. “The gringos are behind this plan,” Maduro claimed.