"Kofi Annan reluctantly accepts the withdrawal of Cyril Ramaphosa from the role of chief mediator. Withdrawal is a result of reservations expressed by the government," a U.N. official said in a statement to media.

Annan mediated an agreement between Kenya's feuding parties on Friday to take steps to end violence that has killed around 900 people and uprooted 300,000 more since President Mwai Kibaki's disputed re-election on December 27.

As part of the agreement, which included a commitment to resolve the immediate crisis within 15 days, Annan's mediation team unanimously chose Ramaphosa to lead talks in the longer term to address Kenya's ethnic and land issues.

Government officials have complained that Ramaphosa, the chief negotiator for South Africa's African National Congress in talks that produced a peaceful end to apartheid in 1994, has business links to Kenyan opposition leader Raila Odinga.