Some of the dead soldiers had been based in Kabul's Warehouse camp
Ten French soldiers have been killed in an ambush by Taleban fighters east of the Afghan capital, Kabul.
A further 21 French troops were wounded in one of the heaviest tolls suffered by the Nato-led International Security Assistance Force (Isaf).
French President Nicolas Sarkozy has announced he will travel to Kabul to assure troops of his support.
The deaths come amid warnings that insurgents are closing in on the capital city.
The loss of life is thought to be the heaviest suffered by the French military since 58 paratroopers were killed in Beirut in 1983.
The BBC's Emma-Jane Kirby, in Paris, says news of the deaths is bound to provoke anger in France, where about two-thirds of people say they are opposed to any French involvement in the conflict.
But President Sarkozy insisted France remained committed to the fight against terrorism, and that the mission in Afghanistan would continue.
The French troops were caught up in fighting that started on Monday in the area of Sarobi some 50 km (30 miles) east of Kabul.
French defence officials said about 100 soldiers - from France, the US and Afghanistan - were on a reconnaissance mission when bad road conditions forced them to stop their vehicles.
A group of French soldiers was sent ahead on foot to check the terrain, but they were ambushed by Taleban fighters and nine were killed.
A tenth French soldier was killed when his vehicle overturned on the road.
An Afghan intelligence officer told the BBC the troops had been ambushed from several directions.
"The Taleban and al-Qaeda forces used heavy machine guns and other weapons. They fired from mountains and gardens," he said.
The fighting went on for 24 hours and it is understood that reinforcements had to be called in to airlift the troops to safety.
The French recently took over control of the Kabul regional command which includes Sarobi.
Wave of attacks
France has about 3,000 troops deployed in Afghanistan. The French news agency AFP reported that Tuesday's deaths brought to 24 the number killed since 2002.
Leaders from countries including the UK and Italy - both of which have sizeable troop deployments in Afghanistan - paid tribute to the French soldiers.
19 August 2008: 10 French troops killed and 21 wounded in ambush east of Kabul
13 July 2008: Nine US soldiers killed and 15 wounded in attack on base in Kunar
28 June 2005: Rocket-propelled grenade downs US helicopter in Kunar, killing all 16 servicemen aboard
"Theirs was a sacrifice not just for France but for all of us who want to help the Afghan people build a better future," said UK Prime Minister Gordon Brown.
Italian Prime Minister Silvio Berlusconi said the soldiers had died "defending democracy and freedom in Afghanistan".
The ambush came amid signs of deteriorating security in Afghanistan.
Despite increased security in Kabul, two rockets were fired on the city overnight, landing close to the Isaf headquarters.
In the southern province of Kandahar a Nato patrol was struck by a roadside bomb.
And in the south-eastern province of Khost six suicide bombers were killed while attacking a Nato military base, Camp Salerno, Nato says.
Isaf confirmed that Camp Salerno had been attacked by rockets or mortars, and that a number of suicide bombers had tried to storm the base.
On Monday, nine Afghan civilians were killed when a suicide bomber rammed a car into the gate of the same base.
ISAF REGIONAL COMMANDS AND TROOP NUMBERS
Countries contributing more than 1,000 troops
Australia - 1,100
Canada - 2,500
France - 3,000*
Germany - 3,370
Italy - 2350
Netherlands - 1,770
Poland - 1,140
UK - 8,530
US - 14,000*
Sources: Isaf, June 2008. *France and US government statistics.
Figures are approximate