Sarkozy made the statement at talks with President Hamid Karzai during his five-hour surprise visit, when he also met with French troops deployed in the capital, Kabul, to give them his Christmas greetings.
He said a decision on troop numbers will be made shortly. France currently has about 1,600 troops in Afghanistan as part of a 40,000-strong NATO force. The country has seen a rise in violence in the last two years, its worst crisis since the Taliban regime was overthrown in the 2001 U.S.-led campaign.
Sarkozy also pledged to step up assistance in training military personnel for the Afghan army and police.
France plans to build an airbase near the southern city of Kandahar and deploy six Mirage bombers and four Rafale fighters there to support NATO military operations in Afghanistan.
But the two presidents also said peace talks with insurgents should not be underestimated either.
Italian Prime Minister Romano Prodi is also expected to arrive in Afghanistan to congratulate 2,000 Italian troops on Christmas.
