Kenyan Opposition leader Raila Odinga says President Mwai Kibaki is in office illegally and that he will not negotiate with the government until the president steps down.

Mr. Odinga made the comments to reporters Saturday in response to Mr. Kibaki's announcement that he is ready to form a national unity government with the opposition in an effort to end the unrest in the nation.

Mr. Kibaki had met earlier today in Nairobi with the U.S. assistant secretary of state for African affairs, Jendayi Frazer. The U.S. diplomat had also met today with Mr. Odinga.

More than 300 people have been killed in violence that has plagued the nation since last week's disputed elections. Mr. Odinga accused Mr. Kibaki of rigging the December 27th election in his favor.

At the Vatican Saturday, Pope Benedict released a letter to Kenya's Catholic bishops calling for an end to the violence.

Much of the violence is between Mr. Odinga's Luo tribe and the president's Kikuyu tribe. Both sides have accused the other of committing acts of genocide.

The U.N. says the unrest also has forced more than 250,000 people from their homes. Aid workers say they are struggling to get supplies to thousands of people cut off from food and water.

International observers have described last week's vote as seriously flawed. Leaders of Mr. Odinga's Orange Democratic Movement opposition party have called for new elections. The government says it will accept that proposition, but only if a court orders a new vote.

British Foreign Secretary David Miliband issued a statement Friday calling on Kenya's leaders to strike a power-sharing agreement to restore peace in the country.

Mr. Kibaki has said he will talk with political rivals when post-election violence ends.

Kenyan security forces prevented the opposition from carrying out a protest march and rally in Nairobi's Uhuru Park. Another protest called for Friday never materialized.

Some information for this report was provided by AFP, AP and Reuters.