Military officials in Kabul said the fierce clashes started with an attack Monday on an International Security Assistance Force (ISAF) patrol in Sarobi district, about 50 kilometres (30 miles) east of the capital Kabul.

The French source, who requested anonymity, said the soldiers were killed following a "Taliban ambush".

Most of the 3,000 French troops participating in the 40-nation ISAF are in Kabul province, which includes Sarobi, and Kapisa province, northeast of the capital.

It was the deadliest incident for international soldiers in post-Taliban Afghanistan, excluding helicopter or plane crashes. Nine US soldiers were killed in an attack on a base in northeastern Kunar province on July 13.

The incident was the deadliest for the French army since a 1983 bombing in Lebanon in which 58 French parachutists were killed.

In Kabul, ISAF said only that soldiers were involved in a "significant incident with insurgents".

Details could not be released until the fighting was over, it said.

An Afghan military officer said earlier, on condition of anonymity, that 10 ISAF soldiers were killed and another 20 were wounded in the fighting in Sarobi.

Afghan defence ministry spokesman General Mohammad Zahir Azimi would not comment on ISAF casualties but said at least 13 attackers, including a Pakistani national, had been killed.

"Thirteen bodies that the enemy left behind have been recovered but their casualties are much higher," Azimi said. Fourteen other rebels and two Afghan soldiers were wounded, he said.

The extremist Taliban said it had attacked ISAF troops in Sarobi and blown up several vehicles.

"We have inflicted heavy casualties," Taliban spokesman Zabihullah Mujahed told AFP.

The military had responded with air strikes that killed five Taliban and several civilians, he said. Taliban statements are not always accurate and the information could not be independently verified.

Before the latest fighting, about a dozen French soldiers had lost their lives in Afghanistan since the French military arrived in 2003, two years after the fall of the Taliban regime.

Meanwhile, in the eastern town of Khost, ISAF and Afghan troops thwarted an attack on Camp Salerno, the biggest US military base in eastern Afghanistan which is located 30 kilometres (19 miles) from the border with Pakistan.

About 30 fighters tried to storm Salerno, Khost province governor Arsala Jamal told AFP, but ISAF said they were stopped about 1,000 metres (yards) from the camp.

Troops in the base had identified them "posturing to attack the base and engaged them with small-arms fire," the NATO force said. Helicopters arrived soon afterwards and opened fire on the rebels as they tried to flee.

Seven were killed, six of them suicide bombers, ISAF said. Of those, three died after they detonated their suicide vests and three other would-be suicide bombers were killed by troops, who suffered no casualties.

Azimi said 13 attackers were killed.

"Six blew themselves up, six others died in the explosions and one died in gunfire from commandos. Their bodies have been recovered," he said.

"A most intense terrorist mass suicide operation was thwarted," the defence ministry said in a statement.

The Khost governor's office said two children had also been killed in the fighting.

It was the second attack on the base in as many days. A suicide car bomb outside the base on Monday killed 10 Afghan labourers waiting to enter and wounded 13 more.

The Taliban said it was behind both attacks on the camp.

The Taliban were driven from power in a US-led invasion in late 2001 because they would not hand over their Al-Qaeda allies wanted for the September 11 attacks on the United States.

However, they regrouped, with some of them taking refuge in Pakistan, to launch a snowballing insurgency that military officials say is attracting more Arab, Pakistani and other Muslim fighters.

This year has seen some of the deadliest insurgent attacks, with violence said to be up 50 percent in some areas compared with 2007.

A French soldier