Police in the rebel Georgian region of South Ossetia on Wednesday fired warning shots to quell a protest amid a growing political crisis after leadership polls were annulled.

Security forces fired into the air to prevent thousands of angry supporters of female opposition leader Alla Dzhioyeva from forcing their way into the central election commission building amid unusually large protests in the tiny self-declared statelet.

South Ossetia, the focus of the 2008 Georgia-Russia war, was plunged into crisis Tuesday after the region's supreme court cancelled Dzhioyeva's surprise weekend poll victory over a candidate backed by the region's patron Moscow.

As up to 3,000 people rallied for hours on the central square in the main town Tskhinvali despite heavy snow, Dzhioyeva appealed to Russian President Dmitry Medvedev, warning that the region is on the brink of "civil war" and asking to help establish order.

"After many years of lawlessness and arbitrary rule in our country, people supported the opposition candidate and together with her were able to win," she said in her written letter, posted on several news websites.

The supreme court said Dzhioyeva's appeal against its decision would be considered on Thursday.

Outgoing strongman leader Eduard Kokoity meanwhile warned unrest would be dealt with harshly.

"Those who try to destabilise the situation will strictly answer before the law. The South Ossetian leadership will make no compromises and concessions," Kokoity said in comments reported by Interfax news agency.

The demonstration grew smaller in the evening, but hundreds of people remained on the square despite Dzhioyeva's request for the crowd to go home.

Dzhioyeva told journalists after hours of talks that a high-ranking official from Moscow was on the way to South Ossetia. Officially Moscow said it would not intervene but expressed hope the crisis would end peacefully.

"We continue to monitor the tense situation developing in the republic, which definitely raises concern," the Russian foreign ministry said in a statement.

Earlier Wednesday protesters marched through the streets, some carrying Russian and South Ossetian flags and placards with slogans like "Dzhioyeva is the elected president" and "Respect the choice of the people".

Dzhioyeva campaigned on an anti-corruption ticket against the Kremlin's favoured candidate Anatoly Bibilov, accusing the impoverished region's rulers of mismanaging aid money sent from Moscow to rebuild the battle-scarred province after the 2008 war.

Moscow recognised the independence of South Ossetia and another breakaway region, Abkhazia, shortly after the conflict despite other world powers insisting both territories remain an integral part of Georgia.

The supreme court of South Ossetia has scheduled a new election for March 25. The election commission had Dzhioyeva leading Sunday's runoff ballot with 56.7 percent when the vote was annulled because of alleged violations.

Georgia said fair elections were impossible because the territory is "occupied" by thousands of Russian troops stationed there since the 2008 war, when most ethnic Georgian inhabitants were expelled.

"These elections are illegitimate because they are held in conditions of occupation by a foreign country and ethnic cleansing," the head of Georgia's national security council Giga Bokeria told AFP.

The West has also condemned the polls.

"We don't recognise the legitimacy or the outcome of this runoff presidential election. We reiterate our strong support for Georgia's sovereignty and territorial integrity," US State Department deputy spokesman Mark Toner told a news conference in Washington on Tuesday.

The population of the tiny region is also the subject of dispute, with the rebel authorities claiming 70,000 while Georgia says the figure is no more than 15,000.