"Clearly the Kenyan people are expecting more from the coalition government, more unity of purpose, more progress on the reform agenda and more concrete action to end impunity and combat corruption," Annan said after arriving in the Kenyan capital, Nairobi.
"The challenge is to achieve these reforms before the country enters the next electoral cycle in about one year or 18 months' time"
Kofi Annan, former UN secretary-general
"The challenge is to achieve these reforms before the country enters the next electoral cycle in about one year or 18 months' time. That is what I will be discussing here, starting with the two principals."
Anna was due to to meet Kibaki and Odinga on Monday.
The two men have been dogged by accusations that reforms, which were promised to avoid a repeat of the violence, have been delayed and that they have failed to bring those behind the mayhem to justice.
The coalition government has promised a new constitution as well as changes to the police force, judiciary and electoral process.
It has also pledged to tackle disputes over land ownership that fuelled much of the violence.
Annan has been frustrated with the slow pace of progress, and in July handed over a list of the top violence suspects to the International Criminal Court (ICC) in The Hague.
Luis Moreno-Ocampo, the ICC prosecutor, is also said to be running out of patience and said recently that he would pursue charges against those suspected of orchestrating the violence.
He is due to hold "decisive" talks with senior Kenyan officials in the coming weeks.
Surveys suggest that the majority of Kenyans would like some suspects to face the ICC.
An influential Sunday newspaper said in an editorial it was right that The Hague should take over.
But Annan steered clear of the debate over how, or where, the suspects should face prosecution.
"With a sense of urgency and a national spirit it can be done, and done in a reasonable time," he said.
"Achieving reforms would also depend on the strong commitment and political will, I repeat political will, of the coalition parties and parliamentarians."