Nairobi - The party of Kenya's outgoing Prime Minister Raila Odinga, defeated in presidential polls by Uhuru Kenyatta, will file a petition challenging the election result on Saturday, officials said.
Odinga's Coalition for Reform and Democracy (CORD) has alleged fraud in the 4 March vote.
Party officials had been due to file their petition on Friday but said they were delaying the case until Saturday - the final day allowed - as civil society groups were expected to first submit separate petitions.
"It is our wish that our petition is not mixed up," Odinga party official and former land minister James Orengo told reporters on Friday, adding he was "confident of the case we have."
Kenyatta, the son of Kenya's first president, was declared the winner of the presidential poll on 9 March.
Despite concern over the risk of violence ahead of the election, no major incidents have been reported.
Elections in 2007 descended into bloodshed that killed more than 1 000 people and caused hundreds of thousands to flee their homes.
Kenyatta, one of Africa's richest men, faces trial for crimes against humanity at the International Criminal Court in The Hague in July for his alleged role in orchestrating the violence.
The president-elect, who avoided a second-round run-off vote by the slimmest of margins to win a majority with just 50.07%, beat Odinga - his closest rival - by more than 800 000 votes.
Odinga, who won 43.31% of the votes in his third failed attempt at the top job, has said he will respect the decision of the Supreme Court even if it rules against him.