Voters in Comoros have chosen three candidates to compete in the country's second round of presidential elections next month.

Preliminary results from the first round on Sunday show Ahmed Abdallah Sambi, Mohammed Janfari and Ibrahim Halidi holding the top three slots.

Voting was restricted to residents of the island of Anjouan, one of three that make up the Indian Ocean nation.

The three islands reached a power-sharing agreement in 2001 that rotates the presidency every four years among Anjouan, Moheli and Grande Comore. This year, it is Anjouan's turn.

The polls are aimed at breaking a cycle of coups that has plagued Comoros since the country won independence from France in 1975.

President Azali Assoumani is barred from seeking re-election because he is from the main island of Grande Comore. He seized power in a 1999 coup and was elected president in a vote three years later.