There have been huge protests ever since the polls
His reported comments came as hundreds of thousands of opposition supporters returned to the streets of the capital Antananarivo, a day after turning the city into a "ghost town".
According to the Reuters news agency, Armed Forces Minister Marcel Ranjeva told daily newspapers the army would preserve stability.
Supporters of opposition presidential candidate Marc Ravalomanana have held massive and mostly peaceful street protests since December's elections.
But the general strike, which has paralysed the Indian Ocean island, is beginning to have a serious effect on Madagascar, the world's eighth poorest country.
Paralysed island
Mr Ravalomanana, who is also the capital's mayor, says he won the elections outright and accuses incumbent President Didier Ratsiraka of rigging the vote.
The protests on Wednesday came a day after Mr Ravalomanana turned the capital into a ghost town, ordering his supporters to stay indoors all day.
The World Bank and the IMF have estimated that the opposition campaign is costing the island some $12m to $14m a day.
"We are sending a warning to the instigators, the executors, the henchmen - whoever they are and whatever their functions - that we will not fail in our duty to prevent the nation falling into ruin," the armed forces minister was quoted as saying.
But despite the minister's comments, it remains unclear where the loyalties of the army itself lie.
Mr Ravalomanana has repeatedly called on the military to join his protests.
And soldiers apparently sympathetic to the opposition deployed around the state broadcaster last week when opposition supporters marched on the television station.
But the military has by and large stayed out of the latest standoff.
Dialogue call
On Wednesday, Mr Ravalomanana said he had petitioned the High Constitutional Court (HCC) to cancel results of the first round of voting in December, which he insists were rigged.
The court ruled two weeks ago that neither he nor President Ratsiraka had won an absolute majority, necessitating a second round of votes later this month.
Campaigning for the second round is scheduled to begin on Saturday.
Foreign Minister Lila Ratsifandrihamanana said dialogue between the two candidates was essential to bringing a halt to the general strike, which is having a huge impact on the Malagasy economy.
Ms Ratsifandrihamanana, a junior member of the government coalition from a party opposed to the President, said the official results of December's polls should be compared with those collected by the opposition.
"We need a dialogue from both sides," she told the BBC.
"We need to understand what exactly is the problem and why the population is no now on strike."