France is suspending its training operations in Afghanistan and threatening to withdraw its entire force from the country early, after an Afghan soldier shot and killed four French troops and wounded several others.

France's foreign minister described the attack as an "assassination", and said it happened during a training exercise at a base jointly operated by French and Afghan forces.

It marked the second time in a month that French troops were killed by Afghan soldiers. The new attack was among the most deadly days for French forces in the 10 years they have been serving in Afghanistan.

It was the latest in a series of attacks by members of the Afghan security forces against coalition partners that have raised fears of increased Taliban infiltration.

French President Nicolas Sarkozy confirmed the deaths of the French soldiers. Their deaths bring to 82 the number of French troops killed in the Afghan campaign.

"From now on, all the operations of training and combat help by the French army are suspended," Mr Sarkozy said in Paris.

A big part of the French role in Afghanistan recently has been training Afghan troops and police ahead of an expected pull-out of the around 3,600 French troops currently there in 2014.

"If the conditions of security are not clearly restored, then the question of an early withdrawal of the French army would arise," Mr Sarkozy said. "The French army is in Afghanistan at the service of the Afghans against terrorism and against the Taliban. The French army is not in Afghanistan so that Afghan soldiers can shoot at them."

The attack came just weeks after an Afghan army soldier shot and killed two members of the French Foreign Legion serving in the Nato force.

French defence minister Gerard Longuet and the chief of staff of the French army are heading to Kabul. Once they report back, the French government will decide how to proceed.