South Ossetian security forces fired shots into the air as a convoy carrying the Georgian and Polish presidents approached the breakaway territory, forcing them to turn back, a witness said.
A spokeswoman for Georgian President Mikheil Saakashvili said Russian troops manning a checkpoint in the area fired the shots.
The spokeswoman was not present at the scene.
A witness travelling with Saakashvili told the Reuters new agency that uniformed South Ossetians fired the warning shots after the convoy came within 30 metres of the de facto border.
No one was hurt and the convoy turned back. Officials travelling with visiting Polish President Lech Kaczyinski were quoted as saying shots were heard from an unknown direction.
"We were travelling along a mountain road in the direction of Ossetia," Presidential Minister Michal Kaminski was quoted as saying by the Polish PAP agency.
"The cavalcade did not reach its destination and now we are returning to Tbilisi. We heard shots, we do not know what happened."
Russia intervened in Georgia in August to repel a Georgian bid to retake breakaway South Ossetia from pro-Moscow separatists.