Kenyan Prime Minister Raila Odinga is likely to contest provisional election results that seem to give a slim victory to his opponent Uhuru Kenyatta.
While the official results are still awaited, the initial results put support for Kenyatta at 50.03 percent of votes cast. Kenyatta is the son of the country's founding president, Jomo Kenyatta.
"He [Odinga] is not conceding the election. If Uhuru Kenyatta is announced president-elect then he will move the courts immediately," said a close adviser to Odinga, Salim Lone.
"The level of the failures in the system makes it very difficult to believe it was a credible result, and if Uhuru is declared president, Raila will go to court," Lone told the Daily Nation newspaper.
Kenyatta, 51, who also faces international charges of crimes against humanity, reportedly garnered 6,173,433 votes, against his opponent's 5,340,546 votes, out of a total of 12,338,667 votes.
Voter turnout was estimated at around 70 percent. Voting rules in Kenya mean the winner does not to face a second round of voting if he or she secures more than 50 percent of the votes.
Kenyatta's Jubilee Coalition Party has said it is "proud and honoured" over the election results and that they are "grateful" to Kenyans who voted for the party.
If the election victory is confirmed by the electoral body, Kenyatta will have a tough time building relationships with western nations. Both the UK and US governments have expressed serious concern over the prospect of Kenyatta becoming president.
Kenyatta is due to go on trial for alleged crimes against humanity in July at the International Criminal Court (ICC) in The Hague. Violence in the wake of disputed elections in 2007 is believed to have killed over 1,000 people and left thousands homeless. The winner of the contentious election was President Mwai Kibaki, who is stepping down after completing two terms.
This year's election has been marred by technical glitches and delays but the counting process has so far remained transparent, according to international observers.
Supporters of both Odinga and Kenyatta have made allegations of malpractice at the polls. "We have evidence that results we have been receiving have actually been doctored. The national vote-tallying process lacks integrity and has to be stopped," Odinga's running mate Kalonzo Musyoka told reporters.