Uhuru Kenyatta was named the winner of the country's presidential election at the weekend with 50.07 per cent of the vote.
But his opponent Prime Minister Raila Odinga refused to concede, alleging multiple failures in the election process that he said have put Kenyan democracy on trial.
Mr Odinga said the election process had been flawed and announced plans to petition the Supreme Court.
Mr Kenyatta surpassed the 50 per cent level needed to avoid a run-off by just over 8,000 votes out of 12.3 million cast.
The US, Britain and the European Union gave Kenya's new political era a chilly reception.
All released statements congratulating the Kenyan people but none mentioned Mr Kenyatta by name.
The new president faces trial in July at the International Criminal Court over allegations that he orchestrated the murder, forcible deportation, persecution and rape of Mr Odinga's supporters in the aftermath of the 2007 vote.