"Twenty-first Century occupiers, who have no legal, moral or other right to be there and oppress people, are stationed in the heart of Georgia," he said during a joint press conference with Mr Kaczynski.
Mr Kaczynski said it was not clear if the gunfire was aimed at the motorcade or into the air.
He added that he had travelled to the remote checkpoint because he wanted to see whether Russian troops were in places they should not be according to the terms of the ceasefire agreement.
Russian peacekeepers in South Ossetia denied firing on the convoy.
"The claims that Russian servicemen were implicated in the shelling of the cortege do not correspond with reality," a Russian spokesman was quoted as saying by Interfax news agency.
Russian state media also reported South Ossetian denials.
"The South Ossetian side has nothing to do with it," said South Ossetian spokeswoman Irina Gagloyeva told RIA Novosti.
The purpose of the presidential visit was to underline the precarious situation in which many Georgians find themselves three-and-a-half-months after the war, says the BBC's Tom Esslemont in Tbilisi.
Now President Saakashvili is using the incident as a means to highlight what he says is the need for continued support from the European Union and the United States, our correspondent adds.
Mr Saakashvili had earlier called for Georgians to unite against a "dangerous threat" from Russia as they did in the bloodless revolution of November 2003.
Saakashvili said the incident was a violation of an EU-brokered ceasefire
Anniversary celebrations this year have been muted after the August conflict with Russia.
The only planned event is a concert at Tbilisi's ornate opera house, and opposition groups have held rallies calling for Mr Saakashvili's resignation.
One of Mr Saakashvili's former allies, Nino Burjanadze, has used the anniversary to launch a new opposition party, accusing the president of authoritarianism.
On 7 August, Georgia tried to retake South Ossetia by force after a series of lower-level clashes with Russian-backed rebels.
Russia launched a counter-attack and the Georgian troops were ejected from both South Ossetia and Abkhazia, a second breakaway region, days later.
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