France has suspended its training programmes for Afghan troops after an Afghan army soldier opened fire in eastern part of the country, killing four French soldiers, according to both NATO and Afghan accounts.
Sixteen more members of the French armed forces were injured in Friday's shooting, in the Tagab district of Kapisa province, north of the capital Kabul, a security official told the AFP news agency on condition of anonymity.
The attack took place inside the base during a training session conducted by French forces.
French troops had surrounded their base in Kapisa and were not allowing any Afghan soldiers to approach, a security source told AFP.
The shooter has been arrested by NATO's International Security Assistance Force (ISAF), the source said.
Nicolas Sarkozy, the French president, said he was mulling an early withdrawal of French troops out of Afghanistan.
"The French army is 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.
"Between now and then all training, joint combat operations by the French army are suspended," Sarkozy said.
Hamid Karzai, the Afghan president, expressed his "heartfelt condolences" over the incident. Rahim Wardak, his defence minsiter, has ordered an immediate investigation.
NATO chief Anders Fogh Rasmussen also expressed his condolences.
"This is a sad day for our troops in Afghanistan and the French people," Rasmussen told reporters.
But Rasmussen warned against seeing a new trend of insider attacks on the 130,000-strong foreign contingent in Afghanistan.
"Such tragic incidents are terrible and grab headlines but they are isolated. The reality is that every day 130,000 ISAF troops from 50 nations fight and train with over 300,000 Afghan troops. That takes a lot of trust among a lot of soldiers," he said.
Afghan soldiers 'gutless'
There has been a number of incidents of Afghan soldiers turning their weapons on members of the NATO-led foreign force fighting an uprising by the Taliban.
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.
The latest deaths brought to 82 the number of French soldiers killed in Afghanistan since French forces deployed there at the end of 2001. Last year was the deadliest so far, with 26 killed.
France has about 3,600 soldiers serving in the country, mainly in the provinces of Kabul and Kapisa.
Al Jazeera's Jacky Rowland, reporting from Paris, said "depending on the outcome of their inquiry the president will decide" whether to pull out two years earlier than planned or resume French operations.
Though NATO does not publicly release figures for coalition soldiers killed at the hands of the Afghan soldiers they train and fight alongside, a 2011 report - A Crisis of Trust and Cultural Incompatibility - shows three dozen attacks against coalition forces by Afghan soldiers since 2007.
"US soldiers don’t listen, they are too arrogant," said one of the Afghan soldiers surveyed, in the report.
Another said: "They get upset due to their casualties, so they take it out on civilians during their searches."
An American soldier was quoted in the same report saying Afghan soldiers "are pretty much gutless in combat; we do most of the fighting".
The shooting of the French soldiers marked the culmination of a week of violence, including a helicopter crash in southern Afghanistan, killing six American soldiers, on Thursday.
In a brief statement, ISAF said early on Friday that there was no enemy activity in the area at the time of the crash on Thursday night.
The cause of the crash is still being investigated, NATO said.
Earlier on Thursday, seven civilians were killed outside a crowded gate at Kandahar Air Field, a base for US and NATO operations, after a suicide attacker set off a vehicle laden with explosives.
Eight people, including two civilians and two Afghan soldiers, were wounded in the incident near the entrance of the Kandahar airport, a provincial spokesman, Zalmay Ayoubi, told local Afghan media.
The Taliban claimed responsibility, saying they were targeting a NATO convoy.
It was the second suicide bombing in as many days in southern Afghanistan, officials said. ISAF said no NATO troops were killed. It does not disclose information about injured troops.