Kenya's outgoing Prime Minister Raila Odinga, defeated in last week's presidential polls by Uhuru Kenyatta, was preparing his Supreme Court appeal alleging fraud, officials said Monday.
"Among other things, they are questioning the one million voters who voted only for president and no other position," said a close aide to Odinga, adding that the appeal would likely be filed at Kenya's highest court on Wednesday.
Odinga is also expected to request a "forensic audit of manual and electronic data", including investigations into the alleged "drastic reduction and rise" of votes in some constituencies after the official register was closed, the aide added.
Kenyatta, 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 in the March 4 poll in his third failed attempt at the top job, has said he will respect the decision of the Supreme Court even if it ruled against him.
He has also called for his supporters to allow the legal process to run its course, warning shortly after Kenyatta was declared president-elect on Saturday that "any violence now could destroy the country forever".
Kenyatta, one of Africa's richest men, faces trial for crimes against humanity in July at the International Criminal Court (ICC) over his alleged role in orchestrating the bloody violence following the 2007 contested elections.
More than 1,100 people were killed and over 600,000 fled their homes in one of the worst bouts of ethnic bloodletting in Kenya.
Odinga legally has until Saturday to file his petition -- seven days from the results -- with Supreme Court then having 14 days to make their ruling.
Kenya's Chief Justice Willy Mutunga has the power to order a recount, order a whole new election or dismiss the petition.
If the petition is dismissed, Kenyatta would be inaugurated as Kenya's fourth president one week later, suggesting a possible ceremony in early April.
Kenyatta has offered "my older brother" Odinga an olive branch, telling thousands of his party loyalists he wanted to work with him "in moving our nation forward."
He also called on his celebrating supporters to be "modest in our victory."