Enlarge By Nashanuddin Khan, AP Two dead bodies of suicide bombers are seen by local residents in the site where they detonated themselves in Khost city, eastern Afghanistan. SUROBI, Afghanistan (AP)  Insurgents ambushed a group of elite French soldiers as they climbed a mountain pass, killing 10 troops in a militant stronghold outside the capital, officials said Tuesday. Soldiers from the paratroops and Foreign Legion were among the dead Monday — the biggest single combat loss for international forces in Afghanistan in more than three years. French President Nicolas Sarkozy announced that he would immediately fly to Kabul to reassure French troops and that "France is at their sides." The soldiers were on a reconnaissance mission in the Surobi district, about 30 miles (50 kilometers) east of the Afghan capital, when they were ambushed Monday afternoon. NATO sent backup and said a "large number" of the attackers were killed in the three-hour gunbattle. France's top military official, Gen. 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," Sarkozy said in a statement. He added: "My determination remains intact." The attack, which also wounded 21 French troops, could heighten domestic opposition to Sarkozy's plan to boost the French contingent by some 700 troops by the end of this month for a total of 2,600. U.S. President George W. Bush, who was briefed at his Texas ranch about the deaths, sent his condolences to the families of the dead and wounded French soldiers. White House spokesman Gordon Johndroe said Bush offered "heartfelt thanks for the sacrifice that they are making and the commitment that the French are making to help secure Afghanistan." Qazi Suliman, the district chief in Surobi, said 13 militants were reported killed. One Western official described the attacks on the French as "complex." 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. The French patrol, which also had Afghan army troops attached to it, was ambushed around 3 p.m. on Monday near Uzbin, the area that straddles the provinces of Kabul and Laghman, said Abdul Jalil Shamal, the district police chief. French troops in armored vehicles drove toward the scene of the battle on Tuesday, while other troops blocked civilian traffic from accessing the area. Witnesses reported many helicopter flying over the region's mountainous peaks. The area is known as a militant redoubt, and there has been a number of clashes in recent months. France will have some 2,600 troops in Afghanistan by the end of this month, after President Nicolas Sarkozy pledged in April to send 700 more troops to eastern Afghanistan. The French troops have been mostly based in Kabul up to now. The deaths of 10 soldiers would be the deadliest attack against international troops since June 2005, when 16 American troops were killed in Kunar province when their helicopter was shot down by a rocket-propelled grenade. In July of this year nine U.S. troops died when insurgents attacked a base on the Kunar-Nuristan border in eastern Afghanistan. The Surobi battle was the highest French military death toll in an attack since clashes in Bouake, Ivory Coast, in 2004. Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more