Madagascar's government said it has replaced the mayor of the capital, Andry Rajoelina, who is trying to topple the president.
Officials offered no explanation for the dismissal that was announced Tuesday.
Rajoelina has been leading protests against President Marc Ravalomanana, who he accused of being too authoritarian. At least 68 people were killed when the protests turned violent last week.
On Saturday, the mayor declared himself in control of Madagascar's affairs, and Tuesday he said would form a transitional government on Saturday if the president refuses to resign by then.
But President Ravalomanana has said that he remains in charge of the country.
Meanwhile, police and media reports said six opposition leaders were arrested Monday as they prepared for a rally in the northeastern port city of Toamasina. The Reuters news agency quoted a police official who said the men were arrested for holding a pubic meeting without a permit.
Rajoelina had called for a general strike, but on Monday businesses, schools and government offices in the capital were open as usual. Crowds at his rallies have grown progressively smaller in recent days.
Tensions began several weeks ago when the government shut down a television station run by Rajoelina, a decision that has been reversed.
The international community has urged the president and the mayor to begin a dialogue.
Some information for this report was provided by AFP, AP and Reuters.