President Nicolas Sarkozy on Friday suspended French military training operations in Afghanistan and said he was mulling an early withdrawal after a renegade Afghan soldier shot dead four French troops.

"The French army stands alongside its allies but we cannot accept that a single one of our soldiers be wounded or killed by our allies, it's unacceptable," Sarkozy said, dispatching Defence Minister Gerard Longuet to Afghanistan.

Longuet and army chief of staff Admiral Edouard Guillaud will establish the circumstances of Friday's shooting in which an Afghan soldier opened fire on French troops, killing four and wounding eight, before he was arrested.

"Between now and then all training and joint combat operations by the French army are suspended," Sarkozy said.

"If security conditions are not clearly established, then the question of an early return of the French army will be asked."

Training Afghan forces and accompanying them into battle against rebels is the core of the French mission within the NATO-led coalition in Afghanistan, the force having already scaled down its own operations.

France has about 3,600 soldiers serving in the country, mainly in the provinces of Kabul and Kapisa, the scene of Friday's shooting.

Their deployment is deeply unpopular in France, and Sarkozy is facing a tough reelection battle in less than three months.

French troops have fanned out around their base in the eastern province and are not allowing any Afghan soldiers to approach, a security source told AFP. Longuet said that eight soldiers were wounded in the attack, including one seriously, revising down an initial wounded toll of 16.

"We will have to make a difficult decision in the coming days. But I must assume my responsibilities before the French people and before our soldiers," Sarkozy said.

The French force currently in Afghanistan will be reduced to 3,000 by late 2012, with 200 due to leave in March. NATO is due to hand security over to Afghan forces before withdrawing all its combat troops by the end of 2014.

NATO chief Anders Fogh Rasmussen on Friday expressed his condolences after the shooting, but insisted the attack was isolated.

"This is a sad day for our troops in Afghanistan and the French people," Rasmussen told reporters during a visit to fellow NATO member Latvia.

"I would like to express my condolences for the four French soldiers who were killed today and my sympathy to those who were wounded," he said, warning against seeing a new trend of attacks from renegade Afghan troops.

"Such tragic incidents are terrible and grab headlines but they are isolated," he said, noting that 130,000 NATO-led international forces are still serving alongside more than 300,000 Afghans.

The latest deaths brought to 82 the number of French soldiers killed in Afghanistan since French forces deployed there at the end of 2001.

Suicide attacks, roadside bombs and insurgent attacks had a heavy toll on French troops in 2011. A total of 26 were killed, the most in a single year during the 10-year war.

The shooting was the latest in a string of incidents of Afghan soldiers turning their weapons on members of the foreign force fighting an insurgency by hardline Taliban Islamists.

Last month, two soldiers with the French Foreign Legion serving in Afghanistan were shot dead by a man wearing an Afghan army uniform during a mission in Kapisa, site of the main French base in Afghanistan.

The Taliban claimed responsibility for that attack.

In April last year eight US soldiers were killed in a shooting at a military airport in Kabul, but a Pentagon report this month said the killings were the actions of a disturbed Afghan military officer who acted alone.

While some attacks have been claimed by the Taliban, others have been put down to arguments or personal animosity between soldiers from the two forces serving together.