The operation is aimed at re-establishing the sovereignty of Afghan security forces in the north of the Uzbin Valley", said Col Benoit Durieux of the French Foreign Legion.

The force includes 800 French legionnaires, together with US and Afghan soldiers. Ten French soldiers were killed in the area in August 2008 when they were ambushed by Taliban fighters.

A further 21 French troops were wounded, in one of the heaviest ballets the Nato-led International Security Assistance Force (Isaf) has faced.

The fire exchange lasted for around 90 minutes. A French spokesman said at least one Taliban fighter had been killed and three were wounded.

 The French codename the offensive Septentrion, following weeks of negotiations with local villagers.