France will pull a quarter of its troops out of Afghanistan by the end of next year.
President Nicolas Sarkozy made the statement during an unannounced flying visit to the country.
Sarkozy was due to spend just five hours there and had meetings scheduled with Afghan leader Hamid Karzai and General David Petraeus.
There are currently about 4,000 French soldiers in Afghanistan. The remaining troops will be based in Kapisa province. French soldiers have been involved in the military campaign against Taliban insurgents since 2001.
Some political commentators have said the early pullout may give Sarkozy a boost ahead of presidential elections next April.