Dissident troops in Madagascar say they have moved tanks into the capital amid a violent power struggle between the president and opposition leader.
President Marc Ravalomanana issued a radio appeal urging civilians to help defend the presidential palace.
The military police and some army units are working together - but are refusing to take orders from the government.
President Marc Ravalomanana has been in a power struggle for weeks with former Antananarivo mayor Andy Rajoelina.
Negotiations between the president and Mr Rajoelina planned for Thursday and Friday were called off.
The opposition leader is apparently attempting to establish a parallel government by naming an alternative cabinet.
Correspondents say that as the country sinks into political chaos it is not clear who has the upper hand, and exactly what role the mutinous soldiers intend to play.
Col Noel Rakotonandrasa, a spokesman for the mutinous soldiers, said tanks had been deployed in Antananarivo, known locally as Tana, as a precaution to intercept any mercenaries hired by the government.
Opposition supporters have said they fear the president might bring in mercenaries to counter mutinous troops.
"We moved tanks into Tana during the middle of the night. They're not on the streets but at a secret location," Col Rakotonandrasa said.
The Associated Press news agency quoted the colonel as saying the tanks had been moved "to barracks where they are needed".
Col Rakotonandrasa was quoted as denying rumours the dissident troops were planning to march on the palace.
At least 100 people have died during opposition protests that began in late January.
The US ambassador to Madagascar warned on Wednesday that the Indian Ocean island nation was on the verge of civil war.
Mr Rajoelina is a 34-year-old former DJ and businessman who was sacked as mayor of the capital last month.
He went into hiding last week after the security forces tried to arrest him.
Col Andre Andriarijaona (2nd right), 11 March 2009
Col Andriarijaona (2nd right) has said he does not intend to seize power
Mr Rajoelina's current location is unclear. A French official said he had left the French embassy, where he had sought refuge earlier in the week.
On Thursday, military police leader Gen Pily Gilbain said his forces were backing the new head of the army, Col Andre Andriarijaona, who earlier in the week ousted his predecessor appointed by the president.
But state radio reported on Thursday that Adm Mamy Ranaivoniarivo, who resigned as defence minister two days earlier apparently under pressure from mutineers, was back in his post.
Under President Ravalomanana Madagascar's economy opened to foreign investment, particularly in the mining sector, BBC World Affairs correspondent Adam Mynott reports.
But he says little of this has tricked down to the 70% of Madagascar's 20 million population who live on incomes of less than $2 (£1.40) a day, and the opposition has tapped into growing resentment.
Meanwhile, foreign governments are advising people not to travel to Madagascar and the tourist industry, a vital source of revenue, is reeling. More than 95% of foreign bookings have been cancelled.