A Russian military convoy advanced to within 55 km (30 miles) of Tbilisi on Friday, from the Russian-occupied town of Gori inside Georgia proper, a Reuters witness said.
The incursion marked the closest troops have come to the Georgian capital, and coincided with a visit by U.S. Secretary of State Condoleezza Rice to push a French-brokered peace plan to end the Russia-Georgia conflict.
The convoy of 10 armored personnel carriers (APC), mounted by soldiers, was initially shadowed by three low-flying Russian combat helicopters as it pulled slowly past Georgian police and then army checkpoints without stopping.
The helicopters then left the convoy.
The vehicles halted in the village of Igoeti on the main highway to the Georgian capital. Their purpose was not clear. Several APCs pulled into side roads.
Russian troops this week pushed out of breakaway South Ossetia as far as Gori, 25 km (15 miles) from the separatist territory, after Georgian forces withdrew under heavy fighting.
Moscow says it is securing Georgian military installations and abandoned arms dumps. On Thursday, Russian troops were spotted in Gori, the Black Sea port of Poti, and the western town of Zugdidi, which lies near another breakaway region, Abkhazia.
Georgia has been calling for the Russian troops to pull back from Gori, alleging that militias from over the border in the North Caucasus have moved in behind them and are looting and burning Georgian villages north of the town.