A fiery leftist who claims he was robbed of victory in Mexico's presidential election led hundreds of thousands of people in a protest march on Sunday (July 30) and vowed they would occupy the capital until all the votes are recounted. Andres Manuel Lopez Obrador told his supporters the occupation would include Mexico City's imposing Zocalo square, one of the largest in the world, and main roads running through the city centre. He urged them to stay there until Mexico's top electoral court orders and carries out a recount of all the votes. The protest, which could last for weeks, is certain to cause traffic chaos in the capital, including the main financial district. It marks the start of a campaign of civil disobedience to protest alleged fraud in the July 2 election. "I propose we stay here day and night until the votes are counted and we have a president-elect," Lopez Obrador said, adding that he would live with thousands of supporters in the Zocalo until the election fight is resolved. The Zocalo was once the centre of the Aztec empire and is still the heart of modern Mexico, home to the National Palace and the capital's main cathedral. Mexico was plunged into a political crisis by the razor-thin election margin of victory, which saw conservative ruling party candidate Felipe Calderon beat Lopez Obrador by around 244,000 votes out of more than 41 million cast. Lopez Obrador, an austere former mayor of Mexico City who promised to help the poor with ambitious infrastructure and welfare programs, claims the vote counts were tampered with at more than half the country's roughly 130,000 polling stations. He is challenging the result before the electoral court, and says he will only accept it if there is a full recount. Critics accuse the leftist of holding Mexico to ransom. Calderon insists the vote was clean and no recount is needed, and European Union observers have said they found no evidence of foul play. "I had powerful adversaries, very charismatic but I won cleanly and we will not permit that those votes by millions of Mexicans be canceled by demagogy and no reason. That would finish not only with a democratic election but with the future of the country," Calderon said on Sunday after visiting the electoral tribunal. It was the third major protest rally in the last three weeks, and one of the biggest in Mexican history. City police said more than 1 million people joined the march, although their estimates are often exaggerated as the capital is run by Lopez Obrador's party. The fight has split Mexico just six years after President Vicente Fox won an historic election that ended seven decades of one-party rule. Recent polls showed that slightly more than half the country thinks Calderon won cleanly. But more than a third believe there was fraud and half want a recount. Lopez Obrador accuses Fox and his National Action Party of orchestrating the fraud, and called the president a "traitor to democracy" in his speech on Sunday. The seven judges on the electoral court have until Aug. 31 to decide whether there is a case to reopen ballot boxes. Their options range from throwing out Lopez Obrador's case and declaring Calderon the winner, to ordering a partial or full recount or even annulling the vote and calling a repeat. An annulment is thought highly unlikely. Without it, the court must formally declare the president-elect by Sept. 6.