President Nicolas Sarkozy meets French troops
President Sarkozy has pledged France's continued commitment to Afghanistan after visiting French troops and meeting President Hamid Karzai.
He was speaking in Kabul after French troops suffered some of their worst casualties in recent times.
Ten French soldiers were killed and 21 injured in an ambush by Taleban fighters east of the capital, Kabul.
Mr Sarkozy said France was committed to the fight against terrorism, and the mission in Afghanistan would continue.
"Even though the toll is so high, you should be proud of what you are doing. The work that you're doing here is indispensable," Mr Sarkozy told his troops.
"We're going to make sure that the means are put in place to ensure that this doesn't happen again." France has 2,600 troops serving in Afghanistan.
The 10 deaths brought to 24 the number of French troops killed in Afghanistan since 2002, the AFP news agency reports.
There was more violence on Afghanistan on Wednesday. A bomb went off in a busy market in the south-eastern province of Khost.
Officials say that in addition about 19 Taleban fighters were killed in two separate clashes in Khost and in the province of Paktia.
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 arrival of Mr Sarkozy, who was accompanied by French Foreign Minister Bernard Kouchner and Defence Minister Herve Morin, was marked by a flurry of helicopters across Kabul on Wednesday.
On a brief visit on Wednesday, he saw the mortuary at the French camp in the capital and spoke to injured soldiers who were involved in the battle. He also held talks with President Hamid Karzai.
His message was one of support not just to the troops, but also to the Nato alliance and Mr Karzai, says the BBC's Alastair Leithead in Kabul.
The French deployment is not popular at home and the decision was made in April to send extra fighting troops to an even more dangerous part of the country, our correspondent adds.
The French troops were caught up in fighting that started on Monday in the area of Sarobi, some 50km (30 miles) from Kabul.
Mr Sarkozy said the troops were killed in "an ambush of extreme violence"
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 were ambushed from several directions by heavily armed Taleban and al-Qaeda forces.
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 deaths came amid warnings that insurgents are closing in on Kabul.
The French recently took over control of the Kabul regional command, which includes Sarobi.
ISAF REGIONAL COMMANDS AND TROOP NUMBERS
Countries contributing more than 1,000 troops
Australia - 1,100
Canada - 2,500
France - 2,600
Germany - 3,370
Italy - 2,350
Netherlands - 1,770
Poland - 1,140
UK - 8,530
US - 14,000*
Sources: Isaf, August 2008. *US government statistics. Figures are approximate