Taliban insurgents mounted their most serious attacks in six years of fighting, one a complex attack with multiple suicide bombers on a United States military base Monday night, and another by some 100 insurgents on French forces in a district east of the capital, killing 10 French soldiers and wounding 21 others, military officials said Tuesday.

Three American soldiers were wounded and six members of the Afghan special forces in the attack on the base in the eastern province of Khost, bordering Pakistan, the Afghan military spokesman, General Zaher Azimi, said. The battle lasted all night, 10 suicide bombers were killed or blew themselves up, and the insurgents were repulsed without entering the base, he said.

The heavy fighting in the two places marks a sharp escalation in insurgent operations in what is already Afghanistan’s deadliest year since the United States’ intervention in 2001. Insurgents have increased their use of roadside bombs and suicide bombs, but have also shown a growing sophistication with several well-organized, complex attacks employing multiple attackers and different types of weapons systems, NATO officials say.

Before the attack on Monday, 173 foreign soldiers had been killed in Afghanistan this year, including 99 American soldiers and 74 from other nations. The number shows an increase in the rate of killings over 2007, when the total for the year was 232, the highest number since the war began in 2001.

The attack on Camp Salerno in the province of Khost was one of the most complex attacks seen so far in Afghanistan with multiple suicide bombers and a backup fighting force that tried to breach defenses on to the airport at the base. It followed a suicide car bombing at the outer entrance to the same base Monday morning, which killed 12 Afghan workers lining up to enter the base, and another attempted bombing that was thwarted shortly after.

The Taliban claimed responsibility for the attacks in Khost. Their spokesman, Zabiullah Mujahed, reached by telephone at an unknown location, said that 15 suicide bombers, equipped with machine guns and vests packed with explosives, with 30 militants backing them up, attacked the base on Monday night since it was one of the largest foreign military bases in Afghanistan. He claimed some of the bombers got inside the base and had killed a number of American soldiers and destroyed equipment and helicopters. This last claim was denied by General Azimi of the Afghan military.

The fighting in the district of Sarobi, east of the capital, Kabul, on Monday night involved an unusually large insurgent force and resulted in even heavier casualties. Ten French soldiers were killed and 21 wounded, a statement issued by the NATO force in Kabul said, making the fighting the most deadly for foreign troops in Afghanistan since fighting in 2005.

French troops have only recently taken over from American forces in the area, as part of the expanded French deployment in Afghanistan under President Nicolas Sarkozy.

In response to the attack, the French president announced that he would fly late Tuesday to Kabul. “In its fight against terrorism, France has been dealt a harsh blow,” Mr. Sarkozy said in a statement. “My determination is intact. France is resolved to pursue the struggle against terrorism, for democracy, and freedom.”