Kenya opposition presidential candidate Raila Odinga has said the electoral commission’s IT system has been hacked to manipulate the election results.
He rejected early results from Tuesday’s vote indicating a strong lead for President Uhuru Kenyatta.
Kenya’s election chief Wafula Chebukati said he had confidence in the system but the claims would be investigated.
Many fear a repeat of the violence after a disputed election 10 years ago and there have been calls for calm.
More than 1,100 Kenyans died and 600,000 were displaced following the 2007 vote.
Electoral officials say that with 91% of results in, Mr Kenyatta is leading with about 54.5%, to Mr Odinga’s 44.6%.
These results mean Mr Kenyatta appears to be heading for a first-round victory.
Speaking at a press conference Mr Odinga, who heads the National Super Alliance (Nasa), said his supporters should remain calm.
But in the opposition stronghold of Kisumu, in western Kenya, as per the reports a group of several hundred of his supporters take to the streets shouting: “No Raila, no peace”.
They were then dispersed by police using tear gas.
Mr Odinga said that the hackers had gained access to the Independent Electoral and Boundaries Commission (IEBC) computer system by using the identity of the commission’s IT manager, Chris Msando, who was killed last month.
He alleged that the hackers “loaded an algorithm” that allowed them to alter the results and ignore the figures being transmitted from tallying centres around the country.