Venezuela's opposition said on Wednesday they had handed international observers clear evidence of electronic vote tampering that helped President Hugo Chavez win Sunday's recall referendum. Observers, led by former U.S. President Jimmy Carter and the Organization of American States, say they have seen no evidence of fraud so far. But they agreed to audit a sample of the vote results to clear up furious opposition accusations. Opposition leaders on Wednesday charged scores of touch-screen voting machines were pre-programmed with an artificial cap to limit the "Yes" votes to recall Chavez, a former army paratrooper elected in 1998. At least 500 out of 12,000 voting points have so far revealed evidence of tampering, they said. The international community had hoped the vote on whether Chavez should step down would end the bitter struggle over the leftist leader's presidency, but the fresh dispute could inflame tensions in the world's No. 5 oil exporter. "Now, with the cases we have counted, we have more than 500 polling stations where the 'Yes' vote is shown to have had a ceiling, where the voting machines were manipulated," opposition representative Nelson Rampersad told reporters. --MORE 2120 Local Time 1820 GMT