Sarkozy brokered a six-point peace deal four weeks ago, which ended fighting that began when Russia invaded Georgia following Tbilisi's attempt to retake the separatist region by force in August.
Medvedev said on Monday that Russia had agreed in principle to the deployment of 200 EU observers in Georgia by October 1 in order to monitor the ceasefire.
The president said in addition to the deployment of monitors, Russia required a guarantee that Georgia would refrain from using force again and that Sarkozy had assured him of this.
"Russia has received from the countries of the European Union, and France which is chairman of the European Union, a guarantee of the non-use of force by Georgia," he said.
Russia also agreed to remove a key checkpoint from near the port of Poti, in western Georgia, within a week if Tbilisi signed a pledge to not use force against Abkhazia.
Alan Fisher, Al Jazeera's correspondent in Moscow, said: "The Russians have pulled all the aces. They will go when they are ready... they feel they are protecting Russian land. They believe the Georgians have re-armed under the United States.
"As far as South Ossetia and Abkhazia are concerned, they (Russia) have already decided they are going to be independent states. This [the withdrawal] is something Sarkozy can present as a small victory to the EU."
Sarkozy said Barroso, Javier Solana, the EU foreign policy chief, and himself would be travelling to Georgia to discuss the results of the talks with the government there.