The US and Nato have both strongly criticised a decision by Russia, announced last week, to send additional troops to Abkhazia as part of a wider effort to increase Moscow's support for the separatist region.
Coinciding with Friday's meeting, Solana, the EU's highest foreign policy official, made a visit to the heart of the conflict, meeting Abkhaz leaders in their main city of Sukhumi.
Solana said he wanted the EU to get more involved in mediating the conflict.
He said the EU "wants to participate more deeply in settling the conflict".
However, Sergei Lavrov, Russia's foreign minister, who was also present in St Petersburg, reiterated Medvedev's comments and said Russia saw no need for foreign mediation.
"The key to the solution is direct negotiations between the parties," Lavrov said. "The ball is on the Georgian side."
'Spiral of confrontation'
Abkhazia broke away from Georgia in the early 1990s in a conflict that left several thousand people dead and prompted hundreds of thousands of Georgians to flee the region.
Russia has accused Georgia of planning to reconquer the region.
Behind the Abkhazia dispute lie deep tensions over Georgia's bid to join Nato, which Russia considers an encroachment on its sphere of influence.
Nato membership for Georgia would lead to "a very, very negative spiral of confrontation in Abkhazia," Lavrov said.
Tensions have escalated in Abkhazia in recent weeks, with a particularly bitter row over Georgian allegations that a Russian fighter jet shot down an unmanned Georgian surveillance aircraft in April, a claim backed up by a UN report.
Before Friday's meeting, Saakashvili said he would urge Medvedev to revoke an order signed by his predecessor, Vladimir Putin, formalising economic links between Russia and Abkhazia in April.
Medvedev also held talks on Friday with other leaders at the summit, warning Viktor Yushchenko, Ukraine's president, that Kiev should not rush to expel the Russian navy from its base in the southern Ukrainian port of Sevastopol.
Medvedev also warned that Russia would be forced to charge Ukraine double the present amount it pays for gas from next year, saying the move was not political and a result of Central Asian gas exporters raising their prices.
In common with Georgia, Ukraine has also signalled to Russia that it would like to join Nato.