RIO DE JANEIRO, June 25 (Reuters) - A Brazilian congressman who has denounced alleged wrongdoing in a 1.6 billion reais ($323 million) COVID-19 vaccine contract signed by Brazil"s government arrived at a Senate commission inquiry on Friday wearing a bullet-proof vest for safety. Congressman Luis Miranda and his brother Luis Ricardo Miranda, the whistleblower at the Health Ministry who raised suspicions about the vaccine deal with India"s Bharat Biotech, are the key witnesses in a hearing underway on Friday. The parliamentary inquiry is looking into the government"s handling of the coronavirus pandemic that has killed more than half a million people in Brazil, and accusations that it deliberately delayed securing vaccines to fight COVID-19. Far-right President Jair Bolsonaro, who is under growing pressure to explain the deal with Bharat, said on Friday there were no irregularities in the contract for the Indian drugmaker"s Covaxin shot. "There is nothing wrong with the Covaxin contract, there is no overpricing," he said at a news conference in the interior of São Paulo. The president, who was elected on an anti-graft platform, added that his enemies were trying to stain his government with unfounded accusations of corruption. "I am incorruptible," he said. The allegations regarding the Bharat contract threatens to damage Bolsonaro"s pledge of zero tolerance for corruption in his government. The coordinator of the Senate inquiry has called for protection for the Miranda brothers, and also for the owners of the Brazilian company Precisa Medicamentos, which acts as an intermediary for Bharat. The contract is being probed by federal prosecutors and lawmakers to see why the government struck a speedy agreement with Bharat after COVID-19 vaccine offers from Pfizer Inc (PFE.N) at a lower price were ignored. Luis Ricardo Miranda and his lawmaker brother met with Bolsonaro in March and said they warned him of the suspicious contract, but that nothing was done to investigate the deal. Miranda, head of imports at the ministry, told senators he refused to approve an import license because an invoice for a first shipment asked for up-front payment and was sent by a company not mentioned in the contract, Singapore-based Madison Biotech. Miranda has told prosecutors he was pressured by Alex Lial Marinho, an aide to one of Bolsonaro"s closest allies, former Health Minister Eduardo Pazuello. Miranda"s account was backed up by his congressman brother. The accusations raise awkward questions for Bolsonaro and Pazuello, who is facing criminal and civil investigations into his handling of the pandemic while minister. On Thursday, Bolsonaro said Brazil never paid for or received any doses of the Covaxin shot, and pledged to take action if any corruption was discovered in his government. In a statement issued in India, Bharat Biotech said, "We strongly refute and deny any kind of allegation or implication of any wrongdoing whatsoever with respect to the supply of COVAXIN." It said Madison Biotech was its global sales and marketing unit. ($1 = 4.9477 reais)