Antananarivo - The campaign by Madagascar's opposition to force President Marc Ravalomanana from office suffered a blow when six of its leaders were arrested in the eastern port city of Toamasina, a local newspaper reported.

L'Express daily newspaper said the six opposition figures were nabbed for planning a rally in support of the mayor of the capital Antananarivo, Andry Rajoelina. No official confirmation was immediately available.

Rajoelina accuses the president of authoritarianism and of lacking regard for the plight of the poor, among other things, and is seeking to have him stripped by the courts or by parliament of his powers. The campaign is given no hope in parliament where Ravalomanana's Tiako I Madagasikara (I love Madagascar) has an absolute majority.

On Tuesday, the 34-year-old mayor appealed to a crowd of supporters gathered in the city's May 13 square not to abandon the protest, but their subsiding numbers - around 15,000, compared to over 50,000 eight days previously - points to growing fatigue in opposition ranks.

Many Malagasy soured on the movement over the widespread rioting and looting that followed an opposition rally eight days ago. Over 100 people are reported to have died in the unrest.

Rajoelina plans to take his crusade to oust Ravalomanana on tour Wednesday, starting in the northern town of Antsiranana.

UN Secretary General Ban Ki-moon told an African Union (AU) summit in Ethiopia Monday he was "particularly concerned" about the developments in Madagascar and urged the parties to address their differences peacefully.

AU Commission chairman Jean Ping warned against any unconstitutional changes. (dpa)