"Kibaki is our president!" the supporters shouted in downtown Nairobi before riot police broke up the gathering.
The Dec. 27 election returned Kibaki to power for a second five-year term, with official results putting opposition leader Raila Odinga second in the closest presidential race in Kenya's history. Odinga accused Kibaki of stealing the vote, and protests exploded into riots and ethnic fighting. The death toll has reached 685, the government said Tuesday.
Foreign and local election observers have said the vote count was deeply flawed. Although the electoral chief pronounced Kibaki the victor, he later said he had been pressured to do so and did not know who won.
Efforts at international mediation so far have failed, and CBS news reporter Katherine Arms says observers have little hope that Annan will be able to win concessions from Odinga or Kibaki.
Annan is a smooth diplomat with a cool head, but, says Arms, "both of the characters here are indignant, resolute and unmoving."
Ghanaian President and chief of the African Union John Kufuor left here empty handed after meeting with Odinga and Kibaki, separately, and many think Annan is likely to endure the same fate.
The election has tapped into resentments that resurface regularly at election time in Kenya. But never before has the anger been so prolonged or taken so many lives.
As Kibaki's power becomes more entrenched each day, the opposition's best hope may rest in working out a power-sharing agreement that could make Odinga prime minister or vice president.
Odinga has called for another "peaceful protest" on Thursday, saying, "let them bring their guns and we will face them."
The protest will take place in defiance of a ban and despite the deaths of at least 24 people in three days of protests last week - most blamed on police.
Kibaki's government has put full page advertisements in the newspapers hitting out at Western powers, international media and various human rights groups saying all had contributed to the unrest.
U.S. Ambassador Michael Ranneberger issued a statement which was printed in Tuesday's newspapers, reports Arms.
"My first thought was that these scurrilous propaganda advertisements should not be dignified with a response. Upon further reflection, however, I believe the record should be indeed set straight in the interest of ensuring that the people know the truth.
"It is irresponsible to say, as the advertisements do, that speaking the truth provides incitement to ethnic violence.
"There is compelling evidence of serious irregularities in the vote tallying process from a wide variety of non-partisan sources," Ranneberger said.
Meanwhile, unrest continues with reports of clashes in the Rift Valley region and six reported deaths, among them a man and his two sons killed in the Molo area, where ethnic clashes have been going on for weeks.
So far, 63 people have been killed since Odinga's Orange Democratic Movement called for mass demonstrations last Wednesday to protest Kibaki's reelection.