The French defence minister said Saturday that an Afghan soldier who killed four French troops was a Taliban infiltrator, as he appeared to dampen the prospect of an early withdrawal.

Gerard Longuet flew into Afghanistan for emergency talks and to seek reassurances about safety a day after President Nicolas Sarkozy threatened a swift exit of the 3,600 French troops on the ground fighting the 10-year war.

That came just hours after an Afghan soldier shot dead four unarmed French soldiers at a base where they were having a joint sports session, also leaving 15 French soldiers wounded, eight of them seriously.

"It was evidently a Taliban (who had) infiltrated (the Afghan army) for a long time," Longuet said after meeting General Nazar, commander of the 3rd Afghan army brigade.

The 21-year-old Afghan, who has been identified as Abdul Mansour, was arrested after the shootings.

Longuet said he was an Afghan army deserter who had likely gone to Pakistan, before returning to infiltrate the army ranks. He had been at the Gwan unit for about two months.

The Taliban denied they were responsible.

Insurgents were seeking to "break the confidence between the French forces and the Afghan army", the minister said.

He also stressed that France had the capacity to help the Afghan army to better control its recruits, thanks notably to "new identification techniques", without explaining what those were.

All foreign soldiers are due to leave Afghanistan at the end of 2014, handing over responsibility for security to Afghan forces, but an angry Sarkozy Friday suggested he would pull the French contingent out before then.

"The entire point of this visit is to assess the position that we have to take," Longuet told reporters after arriving in Kabul, appearing to distance himself from the prospect of an immediate withdrawal.

"The mission remains exactly the same, to bring about a stable force" and "to hand over" to the Afghans, he said.

The French role in the US-led NATO mission is unpopular at home and the killings come less than 100 days before presidential elections.

France is one of the largest contributors to the 130,000-strong NATO force fighting the Taliban, who ruled Afghanistan from 1996 until they were ousted from power in 2001 in a US-led invasion.

The minister is to brief Sarkozy on steps being taken by the Afghans to guarantee security conditions for the French soldiers, who were already concentrating on training Afghan forces and accompanying them in combat rather than leading offensives.

Friday's attack was the second time in a month that French troops were shot dead by a soldier of the Afghan army, bringing the country's overall death toll to 82 since troops deployed in 2001.

Longuet, who was accompanied by Chief of Defence staff Admiral Edouard Guillaud, held talks with General Jean-Pierre Palasset, the French commander on the ground, at their main base in eastern Afghanistan.

On Sunday, the French minister will meet Afghan President Hamid Karzai, the Afghan defence and interior ministers, US commander General John Allen and other senior commanders in NATO's International Security Assistance Force.

A classified report leaked to The New York Times says attacks by Afghan soldiers on NATO troops are increasing and are a "systemic" problem, rather than isolated incidents.

The report puts the killings down to a decade of contempt that each side has for the other, and profound ill will among both civilians and soldiers on both sides. It downplayed the role of Taliban infiltrators in the incidents.

On arrival in Kabul, Longuet briefly boarded a French aircraft preparing to repatriate some of the soldiers seriously wounded in Friday's attack.

He said the men were victims of the trust they had in Afghan soldiers.

"They didn't have a chance. This was murder," said Longuet.

Paris immediately suspended French military training and joint combat operations with Afghan troops after the shooting.

The French force is to be reduced to 3,000 by late 2012, with 200 due to leave in March.