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 Friday, officials said.
"We are currently in the final stages of preparing our presidential election petition at the Supreme Court," Odinga party official and former justice minister Mutula Kilonzo told reporters Thursday.
"We want to thank hundreds of brave Kenyans from across the country who have courageously come forward to provide us with information on the anomalies in the presidential elections."
Odinga's Coalition for Reform and Democracy (CORD) has alleged fraud in the March 4 vote..
His rival Kenyatta, the son of Kenya's first president, was declared the winner of the presidential poll on March 9.
Odinga's team complained this week they were blocked from accessing data from the Independent Electoral and Boundaries Commission (IEBC), forcing them to obtain a court ruling Wednesday ordering the documents be released.
The IEBC on Thursday posted more than 33,000 official election documents used to tally the disputed presidential election on its website "for all Kenyans to see".
CORD is expected to request a "forensic audit of manual and electronic data", including investigations into an alleged "drastic reduction and rise" of votes after the official register was closed, an Odinga aide told AFP this week.
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 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 percent, beat Odinga -- his closest rival -- by more than 800,000 votes.
Odinga, who won 43.31 percent 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.