Antananarivo's sacked mayor, Andry Rajoelina, emerged from hiding on Saturday to step up pressure to force the ouster of Madagascar's President Marc Ravalomanana. His supporters said they had taken over the government but the government rejected their assertion.

Reporting live from Madagascar's capital early on Saturday afternoon, a correspondent for BBC World News, the international television news channel, told an anchor that Rajoelina appeared at an opposition rally to demand that Ravalomanana step down from power within four hours.

If the president failed to meet the deadline, a march on the presidential palace was expected in an effort to topple him. However, as the deadline loomed Reuters news agency reported that there was no sign of a march - instead, thousands of Ravalomanana supporters blocked the road to the palace.

In another report, Reuters quoted the opposition's aspirant prime minister, Monja Roindefo, as saying ahead of the rally that the opposition had taken power. "We declare that the transition authority assumes henceforth the powers conferred on the president of the republic," Reuters quoted him as telling journalists.

But the government issued an official communique declaring that "this movement is, and remains a street demonstration, which uses terror and repression to survive." It said the opposition's purported appointment of Roindefo as prime minister was "a violation of the constitution and the principles of democracy."