Delegates at Kenya's constitutional conference have voted to reject a government-backed proposal to retain a president with executive powers.
During the elections, President Kibaki (l) promised Raila (r) the prime minister's post
Kenya's constitutional review process was meant to end last year but ruling coalition feuding led to gridlock.
The voting was marked by chaotic scenes and a subsequent protest from supporters of President Mwai Kibaki.
The decision, if it goes through, puts immense powers in the post of prime minister and in the national assembly.
The BBC's Eric Mnene in Nairobi says Constitutional Affairs Minister Kiraitu Murungi has warned that the government will withdraw its support for the process following the outcome.
The draft report approved by the delegates will be presented before parliament for adoption.
But the government intends to introduce two bills that will give parliament the power to amend the recommendations passed at the delegates conference.
This is contrary to the Constitution Review Act that gives the delegates the final word on the document.
Correspondents say the proposals are controversial and could undermine the coalition government.
Dissident members of the ruling coalition, mainly from the Liberal Democratic Party (LDP), backed the creation of a prime minister's position and have an upper hand at the conference and in parliament.
Public Works Minister and LDP leader Raila Odinga is viewed as the most likely candidate for the post of prime minister.
Delegates have until Friday to wind up the conference.