The results of Kenya's close vote will be announced Saturday, election officials said, as presidential frontrunner Uhuru Kenyatta extended his lead in the final stretch of ballot counting, boosting his chances of avoiding a second round.

"We want to do the last audit and we will do our final declaration tomorrow morning at around 0800 GMT (4pm)," the Independent Electoral and Boundaries Commission (IEBC) said in a statement late on Friday.

"The commission wants to make these announcements when everyone is fresh and the figures and the audit have been done well," it added.

With less than a fifth of constituencies left to report results, Kenyatta had broken the 50-percent threshold needed to avoid a runoff and maintained a clear lead over his rival Prime Minister Raila Odinga.

The latest results from the electoral body put Kenyatta in the lead with 5.8 million votes, or 50.9 percent, with Odinga at 4.7 million votes, or 42 percent of the ballots tallied in 266 out of 291 constituencies.

Kenyatta, the deputy prime minister and one of Africa's richest and most powerful men, faces a crimes against humanity trial in July at the International Criminal Court (ICC) over deadly violence that erupted after the previous elections in 2007.

Should he win, it is unclear how he would combine his presidential duties with a potentially drawn-out court case in The Hague.

Kenyatta's running mate William Ruto faces the same ICC charges of orchestrating murder, forcible transfer and persecution related to the post-poll bloodshed. His trial is set for May 28.

To win the election outright and avoid a second round, a candidate must win more than half of all votes cast, according to the constitution, as well as at least 25 percent of votes in more than half of all 47 counties.

IEBC chief Ahmed Issack Hassan earlier said officials were working "around the clock" to tally the final results "as soon as possible".

The counting process for Monday's election has been marred by technical problems and complaints from both sides.

Odinga's camp has alleged that results had been "doctored", while Kenyatta's party has raised concerns over the inclusion of spoiled ballots in the overall total which could potentially tip the balance in favour of a second round.

The rigging claims, dismissed by Kenya's electoral commission, have added to tensions in a nation still scarred by the weeks of violence that followed the contested polls five years ago, when over 1,100 people were killed and hundreds of thousands were forced to flee their homes.

Odinga also ran for president in 2007 and has always insisted he was robbed of victory, which went to his main rival Mwai Kibaki, who was backed by Kenyatta.

Odinga and Kenyatta -- the son of independent Kenya's founding president -- have both vowed there will be no repeat of the 2007-2008 unrest, and the country has been largely calm in recent days.

Deputy Prime Minister Musalia Mudavadi, trailing in third place with some three percent, conceded defeat Friday, saying he had "misgivings" about the electoral process but also appealing to Kenyatta and Odinga to "keep the peace whatever the outcome of the elections".

The slow-moving vote counting process drew further criticism this week after an expensive electronic system to register and recognise voters -- and later to send results -- suffered widespread failure.

The glitch forced election officials to resort to reading out results hand-delivered by returning officers, with helicopters picking up officials from remote regions.

Initial results sent electronically reported hundreds of thousands of spoiled ballots, but later dropped to tens of thousands after the electronic system was abandoned.

IEBC officials said the drop was due to an error in the electronic system that had multiplied by eight the number of rejected votes.

Odinga's running mate Kalonzo Musyoka on Thursday called for a halt to manual vote counting alleging evidence of rigging, though he gave few details.

But he stressed that the accusations were "not a call to mass action" and that the party was "committed to the principle of rule of law".

Hassan has insisted that the electoral commission has seen no evidence of rigging and said there was "no room to doctor results whatsoever".

A petition to halt the counting process filed at the high court by a civil society organisation on Friday was dismissed as the court said it did not have the jurisdiction.