Defence Minister Gérard Longuet and chief of staff Admiral Edouard Guillaud will be dispatched to Afghanistan to decide whether the security situation is suitable for the French military presence, Sarkozy told an annual meeting with diplomats Friday.
"If the conditions for security are not clearly established, the question of an early withdrawal of the French army will arise," he told them.
France will seek "credible assurances" on the recruitment of Afghan troops, Foreign Affairs Minister Alain Juppé said later.
If they are not forthcoming, French troops may pull out ahead of the present deadline of the end of 2013, he added.
Map of Afghanistan
Four French soldiers were killed and up to 16 wounded, eight of them seriously, when an Afghan soldier opened fire on them on Friday morning after a sport training session.
The International Security Force (Isaf) says that the presumed killer has been detained.
The attack took place in the Tagab valley, where two French soldiers were killed by an Afghan soldier they were training in December.
Tagab military base has been sealed off by French forces.
"The French army stands side by side with its allies but we can't accept that a single one of our soldiers be killed by our allies," Sarkozy said.
- France is responsible for Isaf activity in Kapisa province;
- It was also responsible for Surobi district, east of Kabul, until President Hamid Karzai decreed that Afghan troops should take control there in November last year;
- Eighty-two French troops have died in Afghanistan since the fall of the Taliban in 2001 - 26 of them last year, all in Kapisa;
- There are about 3,800 French troops in Afghanistan, with 400 having pulled out since last October.