The leader of Georgia's breakaway province of South Ossetia says Georgian troops have been firing on the region.
Georgia wants to bring South Ossetia back under its control
President Eduard Kokoity said forces were firing on its main city Tskhinvali and on several villages in the region, Russian news agency Interfax reported.
A Tblisi spokesman denied an attack and accused South Ossetians of shelling villages populated by ethnic Georgians.
The region broke from Georgia after a bloody war in the early 1990s and wants to be united with Russia.
But Georgia's President Mikhail Saakashvili has vowed to bring it back into the fold.
Exchanges of fire
Mr Kokoity claimed it was the beginning of "a well planned aggression" by the central government, Interfax said.
He was quoted as saying the attack involving mortars and artillery started late on Thursday evening and lasted two hours.
Georgian forces had also tried to enter the northern part of Tskhinvali but were stopped by local militia, he said.
Two civilians are reported to have been injured.
The head of Russian peacekeeping forces in South Ossetia was quoted by AP news agency as saying that there was firing between Tskhinvali and a nearby ethnic Georgian village - but that exchanges had died down.
Georgian Interior ministry spokesman Guram Danadze said
Georgian forces did not attack targets in South Ossetia.
"Ossetians were first to fire at Georgian villages but we
did not reply," he said. "Now it is all quiet."