A tank battalion has mutinied at a military base near Georgia's capital, Tbilisi, the government has said. BBC
Tanks and armoured personnel carriers are being sent to quell the rebellion at the Mukhrovani base, witnesses say.
The authorities say the mutiny is part of an attempted coup - linked to Russia and aimed at assassinating President Mikhail Saakashvili.
Russia's envoy to Nato described the charges as "mad". The trouble comes a day before Nato exercises in Georgia.
Russia's President Dmitry Medvedev has condemned Nato for planning military exercises in a country "where there was just a war".
Georgia and Russia have poisonous relations, and fought a war over Georgia's breakaway territory of South Ossetia last August.
In a separate development, Russian Foreign Minister Sergei Lavrov said he would not attend a planned meeting of the Nato-Russia Council later this month following the alliance's expulsion of two Russian diplomats last week.
They were expelled reportedly in retaliation for a spy scandal involving an Estonian official.
'Plotter at large'
The mutiny at the Mukhrovani base, some 30km (20 miles) from Tbilisi, erupted on Tuesday morning, when soldiers began disobeying orders, Georgian officials said.
The soldiers were aiming at "disrupting Nato exercises and overturning the authorities militarily", Georgian Defence Minister David Sikharulidze told Georgian television.
It was not immediately known how many soldiers were taking part in the mutiny.
"The rebellion continues. Law enforcement agents are on the scene," Mr Sikharulidze said.
The mutiny broke out as the government announced it had disrupted a coup plot.
The interior ministry told the BBC that the plotters wanted to destabilise Georgia and assassinate President Saakashvili.
Interior Ministry spokesman Shota Utiashvili said one of the suspected coup leaders - former special forces commander Georgy Gvaladze - was arrested. But he an alleged co-plotter - former chief of special forces Koba Otanadze - was still at large.
The spokesman said the government had been aware of the plot for two months.
The rebellion appeared to be "co-ordinated with Russia", the interior ministry said.
But Dmitry Rogozin, Moscow's ambassador at military alliance, said the mutiny in Georgia was the result of "crazy politics of President Saakashvili".
In a separate development, opposition protests are continuing in Tbilisi.
The demonstrators say they plan to bloc three main roads into the capital later on Tuesday.