Heavily armed insurgents mounted two of the biggest attacks in years on Western forces in Afghanistan, killing 10 French soldiers in a mountain ambush and then sending a squad of suicide bombers in a failed assault early Tuesday on a U.S. base near the Pakistan border.

The audacious strikes suggested a more sophisticated insurgency now willing to launch frontal assaults on U.S. and NATO troops.

Only months ago, militants shied away from large-scale attacks because of the heavy losses they could incur when jet fighters appeared overhead, NATO and U.S. officials said.

But the Taliban and other militant groups appear increasingly willing to commit large numbers of foot soldiers to onslaughts that attempt to overwhelm small groups of U.S. and NATO troops. Just last month, some 200 militants attacked a small U.S. outpost in Afghanistan's eastern mountains, penetrating its perimeter and killing nine U.S. troops.

The suicide attack Tuesday on Camp Salerno, the American base that serves as the logistics hub for the war's eastern front, began just after midnight when a team of attackers dressed in military fatigues were spotted on the horizon.

Afghan and U.S. forces confronted the militants some 1,000 yards from the base entrance, while fighter aircraft attacked from the air. Once surrounded, three suicide bombers detonated themselves, and three more were shot to death, NATO said in a statement. It said a seventh militant was also killed and two NATO soldiers were wounded.

The French soldiers were on a reconnaissance mission when they were ambushed Monday afternoon by a force of about 100 militants in the mountains of Surobi, an insurgent redoubt 30 miles east of the Afghan capital of Kabul.

France's top military official, Gen. Jean-Louis Georgelin, said most of the French casualties came in the minutes after the soldiers ascended a mountain pass. Battles ensued and 21 French soldiers were wounded.

French Defense Minister Herve Morin said about 30 militants were killed and 30 wounded, while Afghan officials said at least 13 militants were killed. Taliban fighters and militants allied to renegade warlord Gulbuddin Hekmatyar operate in Surobi.

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

The high casualties prompted French President Nicolas Sarkozy to immediately board a plane for Afghanistan. France is sending 700 more troops to Afghanistan this month, and the deaths could heighten domestic opposition to the plan.

"In its fight against terrorism, France has just been struck severely," Sarkozy said in a statement, adding: "My determination remains intact."

The back-to-back attacks came only hours after the top U.S. commander in Afghanistan, Maj. Gen. Jeffery J. Schloesser, warned in a rare public announcement that intelligence indicated militants planned to launch attacks Monday.

Seth Jones, an analyst at the Washington-based RAND Corp., said the latest attacks "targeting U.S. and other NATO forces, and Afghan forces, have become larger and bolder, and they include direct, almost conventional-style attacks."

"In late 2006 and into 2007, there was a much greater reluctance among the Taliban and other groups to carry out these conventional-style attacks," said Jones, who travels frequently to Afghanistan. The new operations indicate "they clearly believe they are winning now, and it's caused them to be a bit more audacious."

This year will likely be the deadliest for international troops since the 2001 invasion. Some 178 international forces, including about 96 U.S. troops, have died in Afghanistan this year, according to an Associated Press count. That pace should far surpass the record 222 international troop deaths in 2007.

The attack on Camp Salerno came a day after a suicide car bombing outside the U.S. base killed 10 Afghan civilians and wounded 13 others.

Gen. Mohammad Zahir Azimi, the Afghan Defense Ministry spokesman, offered a slightly different death toll for Tuesday's suicide attack. He said six militants blew themselves up when cornered and seven other militants died in the explosions and a rolling gun battle. Five Afghan soldiers were wounded, he said.

A Taliban spokesman, Zabiullah Mujahid, said 15 militants were dispatched for the attack, and seven blew themselves up, while eight returned to a Taliban safehouse. Mujahid also claimed responsibility for the attack on the French troops.

President Bush, briefed at his Texas ranch about the French deaths, offered a "heartfelt thanks for the sacrifice that they are making and the commitment that the French are making to help secure Afghanistan," said White House spokesman Gordon Johndroe.

State Department spokesman Robert Wood noted that Sarkozy restated his country's resolve to support international forces. "It's important to remember that we are all engaged in a serious effort to bring about a stable Afghanistan," Wood said.

Jones, the RAND analyst, said insurgents are benefiting from a learning process that comes with years of fighting. They are exploiting vulnerable spots more effectively and increasingly using intelligence to their advantage. Safe havens in Pakistan also aid their effectiveness, he said.

An Afghan official said earlier Tuesday that four French soldiers had been captured and killed. But Georgelin, the French general, denied that during a news conference in Paris.

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.

France's new troop deployment will bring the country's force in Afghanistan to 2,600. Sarkozy announced the new forces in April, after the United States pressed its NATO allies to shoulder a heavier part of the combat in Afghanistan.

The French deaths were the highest for that country in an attack since clashes in Bouake, Ivory Coast, in 2004.

Foreign Minister Bernard Kouchner insisted, "France will continue to assume its responsibilities in favor of a democratic and peaceful Afghanistan, and in the fight against terrorism."

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Associated Press writers Jason Straziuso, Rahim Faiez and Fisnik Abrashi contributed to this report from Kabul.