France on Friday warned that it may accelerate the withdrawal of its forces from Afghanistan after four unarmed French servicemen were shot and fifteen others wounded in a killing spree by an Afghan soldier in the northeastern Kapisa Province.

President Nicolas Sarkozy announced the immediate suspension of training and joint combat operations with Afghan forces. “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,” he said. “It’s unacceptable.”

NATO played down the threat. Anders Fogh Rasmussen, the organization’s secretary general, insisted that attacks by Afghan forces are rare. “Such tragic incidents are terrible and grab headlines but they are isolated,” he said before pointing out that there are some 130,000 foreign soldiers serving alongside 300,000 Afghans.

France’s participation in the NATO mission in Afghanistan is unpopular. Sarkozy’s two main challengers for the presidency this year, Socialist Party candidate François Hollande and Marine Le Pen of the far-right and isolationist Front national, have each promised to bring the roughly 4,000 Frenchmen who serve in Afghanistan home. Elections in France are scheduled for April and May.

The president on Friday said that he would dispatch his defense minister to Afghanistan to investigate the shooting. He added that if Afghan authorities cannot ensure the safety of French troops, “the question of an early withdrawal of the French army would arise.”

Afghanistan’s Defense Ministry said the attacker had been arrested and was being questioned. President Hamid Karzai is due to visit Paris next week.

French troops in Afghanistan concentrate on training local security forces which includes accompanying them on patrols. The force is set to be reduced to 3,000 this year before NATO hands over security responsibility to the Afghans in 2014.

The latest deaths brought to number of French soldiers killed in Afghanistan since deployment to 82.