Madagascar will go ahead with a planned presidential election in July, an international mediator said on Sunday, days after the leader of the Indian Ocean island reneged on a promise not to run.

Andry Rajoelina, who seized power in a coup in 2009, had said in January he would not put his name forward, bowing to pressure from regional powers to stand aside to prevent unrest in this year's vote.

But his camp said that deal was broken when the wife of ousted leader Marc Ravalomanana, who had also said he would not contest the vote, said she would stand instead.

A vast island as big as Arizona and Nevada combined, Madagascar has major reserves of oil and minerals but the past four years of political uncertainty have damaged growth and deterred investors.

Former Mozambican president Joaquim Chissano, who has mediated in the crisis since 2009, said he was "uneasy" at what had taken place but had seen nothing to suggest that anyone wanted to set the political process back.

"The Malagasy people want to hold this election on time and find ways to ensure that these elections are peaceful," Chissano told reporters in Madagascar's capital, Antananarivo.

Rajoelina was among 41 people whose names were published by a special electoral court on Friday, confirming them as candidates in the July 24 election.

Chissano said he respected the court and its decision to permit Rajoelina's nomination was irreversible. "It is left to us to hope that there will not be any further irregularities," he said.

Rajoelina's volte-face has raised tensions on the island, whose resources include gold, chrome, uranium, cobalt, nickel and ilmenite, a titanium ore.

The economy shrank 4.6% in 2009, the year of the coup, after growing at 7.1% the year before, and is forecast to expand just 2.6% this year, according to the World Bank.

Rajoelina, a former disc jockey, said his political opponents had nothing to fear. "When you throw yourself into a competition, you have to dare and be afraid of nothing," the president said this weekend.

The Southern African Development Community (SADC) brokered a deal in September 2011 that confirmed Rajoelina as president and allowed for the unconditional return of Ravalomanana.

But the toppled leader remains in self-imposed exile in South Africa, having been blocked by the government from returning on at least two occasions.

He was sentenced in absentia to life in prison after he was accused of ordering elite troops to kill Rajoelina's supporters in the run-up to his overthrow.