Madagascar's outgoing prime minister refused to quit Saturday, endangering a power-sharing agreement brokered by mediators to keep peace on the island.

Monja Roindefo said he does not acknowledge the mediators' appointment on Tuesday of Eugene Mangalaza as a prime minister in the transitional government. Roindefo said he did not feel that all parties involved in the negotiations were given a say in the appointment.

"A simple press release cannot dissolve a government and appoint a prime minister," he said. "It would have at least been necessary that the agreement rising from this consensual and inclusive charter is signed by four principal parties so that can be done. The nonobservance of these conditions means the declaration is null."

Mediators have held three rounds of talks since August to try to resolve the country's political situation. The mayor of Antananarivo, Andry Rajoelina, overthrew President Marc Ravalomanana in March, after weeks of protests left dozens of people dead.

Mediators helped forge a power-sharing agreement in August. They announced last week that Rajoelina would keep his job for now but could not run for re-election. Elections must be held by November 2010.

Rajoelina drew criticism for unilaterally forming a new government in September, violating the August accord.

Ravalomanana, the ex-president said the mediators ignored his party's objections by appointing Rajoelina as president of the transitional government.

Ravalomanana said in a letter sent late Friday to African Union commission chairman Jean Ping that his delegates were excluded from Tuesday's deliberations.