President Uhuru Kenyatta said on Saturday the time for politics is over and the country should focus on development until the next election in 2022.
The government says Raila Odinga’s planned “swearing-in” on Tuesday would amount to treason.
Odinga brought a successful legal challenge against Kenyatta’s August re-election but boycotted the repeat vote in October, saying there had not been enough electoral reforms to guarantee a credible vote.
Odinga says he doesn’t recognise Kenyatta’s legitimacy, but he has said he is open to talks to defuse the current tensions if there is a specific agenda.
Dozens of people have been killed in clashes between security forces and opposition supporters