Kenya's opposition leader has rejected early results of a presidential election after claiming the vote was rigged. Preliminary results show that incumbent president Uhuru Kenyatta, 55, led by 54.8%.

"We reject the results streamed so far and demand IEBC - [Independent Electoral and Boundaries Commission] produces Form 34As from all polling stations before any further results are announced," said Kenyatta's main challenger, the 72-year-old Raila Odinga, in a Twitter post.

Kenya has been marred by violence in the lead up to the election. During the final days of campaigning, a top election official, Chris Msando, was murdered. An autopsy found that Msando had been severely tortured and strangled to death.

"We have our projections from our agents which show we are ahead by far. We fear this was exactly the reason Chris Msando was assassinated," Odinga said at a late night conference on 8 August, according to Sky News.

Following the official's death, the US and the UK issued a joint statement expressing concern over the violence.

"It is critical that Kenya have free, fair, credible and peaceful elections on August 8, and protection for IEBC staff is essential to achieving this goal," read the statement. "We welcome the Government of Kenya's commitment to investigating the murder. We have offered our assistance in the investigation."

Reports says the voting on 8 August was relatively calm. However, some people fear there could be a repeat of the 2007 elections, when tribal tensions culminated in the death of hundreds of people and the displacement of 600,000 people.

Kenyatta, who is seeking a second term in office, hails form the Kikuyu ethnic group, which has supplied three of the four presidents Kenya has had since gaining independence from Britain in 1963.

Odinga comes from the Luo group, which laments a lack of political inclusion and disenfranchisement. The electoral commission has urged people to wait calmly for the official results.

"During this critical phase, we urge all Kenyans to exercise restraint as we await official results from the polling stations and indeed as they start trickling in," it said in a statement quoted by Reuters.

The winner of the election must get more than 50% of the votes as well as one-quarter or more votes in at least 24 of Kenya's 47 counties. If the front-runner falls short of those benchmarks, the two top contenders will have to contest a run-off vote.

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