ODM said Annan told Odinga - who says Kibaki robbed him of victory by rigging -- that he would fly in on Tuesday.
Analysts say Odinga has lost momentum in recent days as Kibaki entrenches himself by appointing the core of a new cabinet, carrying out state functions and recalling parliament.
"MORTAL COMBAT"
Aides to the 76-year-old president, a veteran of Kenyan politics and member of the nation's largest and most powerful Kikuyu tribe, say the opposition's refusal to meet Kibaki face-to-face shows it is not interested in dialogue.
ODM say they will only meet if an international mediator is present.
Kibaki and Odinga, a 63-year-old former political prisoner and wealthy businessman, have not met since the vote, even though they have had close ties in the past including when the opposition leader sat in Kibaki's cabinet from 2002-05.
Around Kenya, there is widespread frustration that the poor have largely paid the price of the unrest while the political elite have stayed in comfortable and well-guarded compounds.
As well as the death toll, which aid groups say will rise to well over 500 and Odinga told Reuters was already nearing 1,000, more than a quarter of a million Kenyans are homeless from ethnic clashes since Kibaki's December 30 swearing in.
"Our leaders are stuck in mortal combat, unable to rise above their ambitions and put the interests of the country and the people first," wrote Daily Nation columnist Lucy Oriang.
The West, including the United States and Kenya's former colonial ruler Britain, has expressed displeasure at irregularities in the presidential vote count, and has been pressing for some sort of power-sharing agreement.
Kibaki has said he will consider a coalition, while Odinga would prefer a re-run of the election.
In the latest statement from abroad, Foreign Secretary David Miliband urged both sides "to engage without any pre-conditions" and "agree on a way to share power so as to reflect the clear democratic will of the Kenyan people".
With key sectors like tourism and commodities hit by the crisis, analysts say the full impact on one of Africa's brightest economies depends wholly on how long it lasts.
