Lawyers representing the Kenyan opposition coalition National Super Alliance filed a petition on Friday with the Supreme Court challenging President Uhuru Kenyatta's re-election, beating a midnight deadline.

A statement from the group's presidential candidate, Raila Odinga, and his running mate, Kalonzo Musyoka, said they turned to the high court because of alleged irregularities in the August 8 presidential vote.

Those included, among others, "numerous instances when their ticket was denied votes and others in which their competitor ... had undeserved votes added to his total," the statement read.

Odinga has rejected the electoral commission's results which say Kenyatta won by roughly 1.4 million votes, with 54% of the vote.

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Odinga claims, without providing proof, that hackers used the identity of a slain election official to manipulate the result in Kenyatta's favour.

The commission has said there was a hacking attempt but it failed, and election observers say they saw no signs of interference with the vote.

At first, the opposition said a court challenge was not an option. But earlier this week Odinga made it clear they had changed their minds, saying, "This is just the beginning. We will not accept and move on."

The Supreme Court has 14 days to rule on the challenge.

Opposition leader Raila Odinga believes he has been cheated for the third time in a row.

Following the disputed 2007 election - which Odinga lost to Mwai Kibaki - politically motivated tribal violence resulted in 1,100 deaths.

When Odinga was declared the loser to Kenyatta in 2013, he took his complaints to the Supreme Court and lost.

Dozens of opposition supporters gathered at the Supreme Court building throughout the day on Friday, waving placards.

Police said they prevented demonstrators from entering the building. Nairobi police chief Japheth Koome said authorities want to ensure the court is secure.

The opposition says 100 people were killed in violence during the election, while police gave a death toll of 10 for Nairobi.

International observers from the European Union and the Carter Center, among others, have called the election result credible.

While praising the conduct of polling day itself, election observers have raised concerns over the transmission and tallying or results with some pointing to discrepancies in numbers and the absence of original polling station tally sheets.