There are conflicting reports about who is in control of Madagascar, an island in the Indian Ocean, where a group of rebel army officers claims to have seized power.
Colonel Charles Andrianasoavina, who made the announcement, was one of the officers behind a coup that brought Andry Rajoelina to power last year.
But Mr Rajoelina denounced the mutineers and said he was unafraid of their threats.
He said the action involved a small group who were trying to stir up trouble on the day of a referendum on a new constitution.
The BBC reports Madagascar has been beset by instability for several years.
President Rajoelina, a former DJ and mayor of the capital city, rose to power on wave of popular support. However, the BBC reports he has been diplomatically isolated since coming to power and has ignored attempts by regional mediators to broker a consensus with the opposition.
The officers said they had dissolved government institutions and formed a military committee.
Colonel Andrianasoavina said the officers wanted national reconciliation, for political prisoners to be freed and for exiles to return to the country.