Madagascar's president has named a new prime minister and fired his former premier, who had refused to step down under the terms of a power-sharing deal aimed at ending nine months of political turmoil, Reuters reported. President Andry Rajoelina, who seized power in a March coup, has endorsed Tuesday's internationally-brokered agreement, which called for Monja Roindefo to be replaced as prime minister by a relatively unknown anthropology professor, Eugene Mangalaza. Rajoelina, who at 35 is Africa's youngest leader, had been under pressure from donors to dismiss Roindefo, who is described by analysts as a heavyweight backer of his power-grab. "Eugene Mangalaza is named prime minister of the transitional government," Haja Resampa, secretary general of the president's office, said in a statement late on Saturday. "All earlier decrees contrary to this appointment are hereby annulled, in particular those of the former head of government, Monja Roindefo." Ousted former president Marc Ravalomanana has refused to accept the power-sharing agreement, which sees his rival retain the presidency of the world's fourth largest island. The instability has hurt economic growth and alarmed foreign investors seeking to exploit its oil and mineral reserves. Rajoelina has said he aims to organise a presidential election before April next year, but has not yet said if he plans to stand as a candidate. Foreign donors say a free and fair ballot will lead to a resumption of aid.