SUROBI, Afghanistan — About 100 insurgents ambushed a group of French paratroopers as they climbed a mountain pass, killing 10 soldiers in a militant stronghold outside the capital. In a separate coordinated attack Tuesday, a team of suicide bombers tried unsuccessfully to storm an American base near the Afghanistan-Pakistan border.

The death of the French soldiers marked the biggest single combat loss for international forces at Afghanistan in more than three years.

The soldiers were on a reconnaissance mission at the Surobi district, about 30 miles east of the Afghan capital, when they were ambushed yesterday afternoon. NATO sent backup and said a “large number” of the attackers were killed in the three-hour gunbattle.

France’s top military official, General Jean-Louis Georgelin, said most of the French casualties came in the minutes after the team was climbing a mountain pass. The fighting lasted into nightfall, he said.

“In its fight against terrorism, France has just been struck severely,” President Sarkozy said in a statement.

But he added, “My determination remains intact.”

The district chief in Surobi, Qazi Suliman, said 13 militants were reported killed. One Western official described the attacks on the French as “complex.”

General Georgelin denied a statement from an Afghan security official that four French soldiers were kidnapped by insurgents and then killed. The Afghan official spoke on condition of anonymity because he was not supposed to release the information.

It was the deadliest attack against international troops in Afghanistan since June 2005, when 16 American troops were killed at Kunar province when their helicopter was shot down by a rocket-propelled grenade.

In July of this year nine American troops died when insurgents attacked a base on the Kunar-Nuristan border at eastern Afghanistan.

The death toll could heighten domestic opposition to Mr. Sarkozy’s plan to boost the French contingent by some 700 troops by the end of this month for a total of 2,600. Mr. Sarkozy said he plans to travel to Afghanistan to reassure French troops and that “France is at their sides.”

In the attack on the American base just a few miles from the border with Pakistan, militants failed to gain entry to Camp Salerno in Khost city after launching waves of attacks just before midnight yesterday, the governor of Khost, Arsallah Jamal, said.

A suicide bombing outside the same base yesterday killed 10 civilians and wounded 13 others.

Ground forces, fighter aircraft and helicopters chased the retreating militants. NATO said its forces identified the attackers about 1,000 yards outside of the base perimeter and launched helicopter gunships.

The Afghan Defense Ministry spokesman, General Mohammad Zahir Azimi, said Afghan soldiers, aided by American troops, chased and surrounded a group of insurgents, and that six militants blew themselves up when cornered. Seven other militants died in those explosions and a rolling gun battle, he said.

“(The Afghan National Army) is saying that anytime we get close to them, they detonate themselves,” Mr. Jamal said.

NATO offered a slightly different account, saying three suicide bombers detonated their vests and three more were shot dead. NATO said seven attackers in total were killed.

At least 13 insurgents and two Afghan civilians died, officials said.

The Taliban appeared to confirm the account. A Taliban spokesman, Zabiullah Mujahid, said 15 militants had been dispatched for the attack on Salerno. Seven blew themselves up and eight returned to a Taliban safehouse, he said.

Mr. Jamal said the bodies of at least two dead militants were outside the checkpoint leading to the base’s airport, both wearing vests packed with explosives, Mr. Jamal said.

Militants have long targeted American bases with suicide bombers, but coordinated attacks on such a major base are rare.

Yesterday, the top American general in the region, Major General Jeffrey J. Schloesser, issued a rare public warning that militants planned to attack civilian, military and government targets during the celebration of Independence Day on yesterday.

More than 3,400 people — mostly militants — have been killed in insurgency-related violence this year, according to an Associated Press count based on figures from Western and Afghan officials.

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Associated Press writer Rahim Faiez in Kabul contributed to this report.