In a separate coordinated attack Tuesday, a team of suicide bombers made an unsuccessful attempt to storm a U.S. base near the Afghanistan-Pakistan border -- one day after a suicide bomber rammed a car packed with explosives into the gate of the U.S. base in Khost, killing 10 people.
The French soldiers, who were from three elite paratroop and marine regiments, were on a mission in the Surobi district, about 30 miles east of the Afghan capital, when they were ambushed on a mountain pass Monday afternoon, the Associated Press reported.
NATO sent reinforcements and said a "large number" of the attackers were killed in a resulting gun battle that lasted into Tuesday.
"The initial patrol was reinforced with quick reaction forces, close air support and mobile medical teams. During the engagement a large number of insurgents were killed," NATO's International Security Assistance Force said in a statement, according to Agence France-Presse
Bryan Whitman, a Pentagon spokesman, said the U.S. provided air support to French forces in the battle. "This was a complex attack involving multiple weapon systems, small arms, mortars, rockets, and lasted for several hours," he said.
Gen. Mohammed Zaher Azimi, a spokesman for the Afghan Defense Ministry, said at least 13 insurgents were killed and 14 were injured in the fighting, the Washington Post reported.
French President Nicholas Sarkozy announced plans to travel to Afghanistan in the wake of the attack, his office said.
"In its fight against terrorism, France has just been struck severely," Sarkozy said in a statement
"My determination is intact. France is determined to continue the struggle against terrorism for democracy and freedom. The cause is just. It is an honor for France and its army to defend it," the French leader said.
An alleged Taliban Web site claimed that 20 U.S. soldiers had been killed in the fighting, which they said started after militants ambushed a convoy of foreign forces late on Monday, Reuters reported. Insurgents commonly refer to all foreign troops as American in communications to media outlets.
The ambush on the French soldiers was the deadliest attack against foreign troops in Afghanistan since June 2005, when 16 U.S. troops were killed in Kunar province after their helicopter was shot down.
The attack also marked the heaviest single loss for the French military since 58 paratroopers serving in a United Nations-led force were killed in Beirut in 1983, the AFP reported.
France has more than 2,000 soldiers in Afghanistan, involved in various NATO and U.S.-led peacekeeping and training operations in the country. Sarkozy decided to send 700 more troops to Afghanistan after a NATO summit in Bucharest in April -- a move that met political and public opposition in France.
In the attempted attack on the U.S. base, militants failed to gain entry to Camp Salerno in Khost city after launching a wave of attacks just before midnight on Monday, Arsallah Jamal, the governor of Khost, told the AP.
ISAF troops killed seven of the insurgents, six of them reportedly suicide bombers, after they spotted them preparing to attack the base. Three American soldiers and six Afghan troops were wounded in efforts to fend off the attack, the New York Times reported.
On Monday, the Taliban took responsibility for an attack in which a suicide bomber drove a car packed with explosives into the gate of the same U.S. base in Khost, killing 10 people and wounding 13.
Monday's assault came amid stepped up security in response to intelligence reports indicating the al-Qaida-backed Taliban were planning attacks to coincide with Monday's celebration of Afghanistan's independence from Britain in 1919.