Nairobi - Kenya's opposition leader rejected preliminary results from a tightly-contested presidential election on Wednesday, decrying the tallying process as a "sham" as President Uhuru Kenyatta surged ahead.The allegation by Kenyatta's longtime rival Raila Odinga raised fears of a possibly violent dispute over the results of Tuesday's election to decide the leader of east Africa's most vibrant democracy."These results are fake, it is a sham. They cannot be credible," Odinga told a press conference in the early hours of the morning as partial results fell quickly via an electronic tallying system aimed at preventing fraud.Results released by the electoral commission (IEBC) showed Kenyatta leading with 55% of the nearly 13 million ballots counted against Odinga's 44%, a difference of nearly 1.4 million votes.Odinga claimed the IEBC had not provided documents that would show how the tallies were arrived at.Ethnically-driven political violence"It is the machine that has voted," Odinga told reporters. "These results are wrong."Odinga, 72, who is making his fourth stab at the presidency, accused his rivals of stealing victory from him through rigging both in 2007 and 2013.In 2007, the disputed vote resulted in two months of ethnically-driven political violence that killed 1 100 people and displaced 600 000 in a major blow to a nation seen as a regional bastion of stability.The contested election in 2013 was taken to the courts, and ended largely peacefully even though Odinga lost.The run-up to this year's vote was fraught with tension, heightened by the torture and murder of Chris Msando, a key administrator of the biometric voting system, whose tortured and strangled body was found on the outskirts of Nairobi earlier this month."We fear that this is the precise reason why Mr. Chris Msando was assassinated," Odinga said, referring to his fraud claims.No stopping resultsThe IEBC was undeterred by Odinga's statements, with commissioner Roslyn Akombe saying that despite a request by an unnamed political party to stop publishing preliminary results, "as a commission we decided that as part of the commitment we made to the voters and the Kenyan people, transparency and accountability are part of them.""This is why, as a commission, we have decided we will continue to display the results," she said.The contest between Odinga and Kenyatta was seen by pollsters as too close to call ahead of the vote.It is the second time the two men have faced off in a presidential election in dynastic rivalry that has lasted more than half a century since their fathers Jomo Kenyatta and Jaramogi Odinga went from allies in the struggle for independence to bitter rivals.The men belong to two of Kenya's main ethnic groups, Kenyatta from the Kikuyu, the largest, and Odinga from the Luo.Both had secured formidable alliances with other influential communities in Kenya, where voting takes place largely along tribal lines.Raphael Tunju, secretary-general of Kenyatta's Jubilee party, shrugged off Odinga's allegations."I don't expect anything else from NASA," he said, referring to Odinga's National Super Alliance party.On Tuesday, Kenyatta urged Odinga to accept the result should he lose."I also want to say that if I lose, I will accept the will of the people," Kenyatta said after voting.A quiet vote Despite reports of some technical glitches and delays, Tuesday's vote went off peacefully, and the IEBC moved quickly to deal with any complaints. A clerk in a polling station where ballot papers were pre-marked as "rejected," was fired, and police arrested another clerk in the port city Mombasa who was caught issuing double ballot papers to certain voters.Shortly before polls closed, NASA put out a statement praising poll officials and security forces, but complained that some of its voters had been turned away.NASA also said it had reports of "pre-marked ballot papers" and attempts to bribe voters.Kenyans voted in six different elections, including several knife-edge races for governor that have fired up local tensions.The opposition also looked set to lose the governorship of the capital Nairobi - which had been seen as a major coup in 2013 - to the ruling party candidate.Kenyatta, 55, is seeking re-election after a first term in which he oversaw a massive infrastructure drive and steady economic growth of more than five percent.But he has been criticised for soaring food prices - with prices jumping 20% year-on-year in May - and massive corruption scandals on his watch.