Madagascar's opposition leader has said he has a mandate to lead a transitional government, hours after troops stormed one of the president's palaces.
Speaking to the BBC, Andry Rajoelina denied that the dramatic seizure of the palace amounted to a coup.
But he said that the President Marc Ravalomanana no longer had the right or the power to run the country.
President Ravalomanana, holed up in another palace, was quoted as saying he was prepared to die with his guards.
The president had also discussed military support with the UN and southern African states, his spokesman told Reuters news agency.
The African Union condemned the "attempted coup d'etat" and called on Madagascar to respect its constitution.
A fierce power struggle on the Indian Ocean island has triggered a military mutiny, looting and violent protests that have left at least 100 people dead since January.
Supporters of the president manned roadblocks outside the capital
On Monday, up to 100 soldiers seized a palace in the centre of the capital, Antananarivo.
Explosions and gunfire erupted as tanks smashed the palace gates. The central bank was also reportedly taken.
The BBC's Jonah Fisher in Antananarivo says people in the capital are trying to conduct their business as usual - but many are clearly in shock after Monday's events.
Earlier, Mr Rajoelina had called for the arrest of the president and won public backing from the self-declared head of the armed forces.
'Power vacuum'
Our correspondent says Mr Rajoelina has wrapped himself in the cloak of democracy, but he wants to replace an elected head of state without going to a ballot.
CRISIS TIMELINE
Dec 2006: Marc Ravalomanana (r) re-elected as president
31 Jan 2009: Opposition's Andry Rajoelina (l) says he is in charge
3 Feb: Rajoelina sacked as mayor of Antananarivo; protests intensify
8 Feb: Security forces fire on opposition rally leaving 28 dead
11 March: Dissident troops oust army chief
15 March: Ravalomanana proposes to hold referendum
The opposition leader, a 34-year-old former disc jockey, says the president is a tyrant who misspends public money.
Mr Ravalomanana's supporters say his rival is a young troublemaker who has not offered any policy alternatives.
Speaking to the BBC's Newshour programme, Mr Rajoelina acknowledged that the president had been elected.
"But we elected him to respect the law and the constitution," he said. "He cannot do whatever he likes with the country.
"So for us this president no longer has the right, nor the power any longer to run the country."
Mr Rajoelina said he wanted a transitional government that would organise elections in the next 18 to 24 months "at the very latest".
"I have the mandate of more than 60 political parties in Madagascar to lead this transition, so it isn't a coup at all," he said.
Col Andre Ndriarijaona, who last week said he had replaced the military chief of staff, told AFP news agency that soldiers had seized the presidency "to hasten Ravalomanana's departure".
'Against bloodletting'
Mr Ravalomanana was hunkered down about 15km (nine miles) from the city centre at the Iavoloha palace, where hundreds of his supporters were camped out.
"The president plans to stay in Madagascar," Andry Ralijaona, a spokesman for Mr Ravalomanana, told Reuters.
"He said this to the presidential guard, who told him he should be placed elsewhere, and he replied 'I will die with you if I have to,'" he said.
But Col Ndriarijaona said: "We are against any bloodletting, so we won't go there until we obtain guarantees on the presidential guard's intentions."
The army has traditionally remained neutral during periods of political volatility since independence from France in 1960.
Col Ndriarijaona claimed it was now almost wholly behind the opposition.
Earlier on Monday, the opposition rejected a proposal from the president to hold a referendum on whether he should complete his term.
Mr Ravalomanana, who was re-elected for a second term in office in 2006, has previously said he wants to remain in office until his mandate expires in 2011.
Under President Ravalomanana, Madagascar's economy has opened up to foreign investment, particularly in the mining sector.
But 70% of the 20 million population still lives on less than $2 (£1.40) a day and correspondents say the opposition has tapped into popular frustration at the failure of this new wealth to trickle down.
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