Kenyan opposition presidential candidate Raila Odinga has rejected early results indicating a strong lead for his rival, President Uhuru Kenyatta.
Mr Odinga told journalists the details were "fake" because the authorities had failed to present documents verifying the results.
Electoral officials say that with 91% of results in Mr Kenyatta is leading with about 54.5%, to Mr Odinga's 44.6%.
Many fear a repeat of the violence after a disputed election 10 years ago in which more than 1,100 Kenyans died and 600,000 were displaced following the 2007 vote.
Mr Kenyatta's lead could mean that he is elected outright. There were eight candidates in all, but apart from Mr Kenyatta and Mr Odinga none polled more than 0.3% of the vote.
The opposition has described the results being released online as a "fraud" because they were not accompanied by original result forms 34A and 34B from the polling stations.
"They are fictitious, they are fake," said Mr Odinga.
He said that the results were "the work of a computer" and did not reflect the will of voters.
"We have our projections from our agents which show we are ahead by far," he added.
Opposition officials have said that, despite assurances from the electoral commission, they still have not received the result forms.The electoral commission has been urging people to wait calmly for the full results of Tuesday's vote.
"During this critical phase, we urge all Kenyans to exercise restraint as we await official results from the polling stations and indeed as they start trickling in," the commission said.
However, it admitted that a lack of mobile data coverage had delayed the delivery of the supporting documents, forms 34A and 34B.
The BBC reports that there had been reports on election day of the failure of some voter-identification equipment. Also, one in four polling stations was apparently without mobile phone coverage, meaning that officials were asked to drive to the nearest town to send results.
The presidential candidates' agents would have "special access" to the forms, though, the electoral commission said.
The Daily Nation newspaper quoted commission head Ezra Chiloba as saying only results supported by the forms had been published.
