President Nicolas Sarkozy of France suspended military operations as part of the American-led coalition in Afghanistan on Friday and said he was considering an early pullout of his nation’s forces after an Afghan soldier shot and killed four French soldiers on a base in eastern Afghanistan.

A US official said Mr. Sarkozy’s threat could lay bare “real cracks in the coalition” at a time when the alliance is seeking a cohesive position to assure the Afghan government of its long-term commitment and to push the Taliban insurgents to negotiate a peace deal rather than continue fighting.

It was the second fatal attack in a month involving an Afghan soldier opening fire on French troops and came at a time when American forces are deeply concerned about increasing numbers of killings of American and other allied forces by the Afghan soldiers they fight alongside and train. It also comes as many European countries with troops here are facing unprecedented economic pressures at home and adds to public questioning of the value of continued involvement in Afghanistan.

If France, the fourth-largest troop-contributing country after the United States, Britain and Germany, were to reduce its numbers more than planned it could spur other countries to follow suit, leaving the Afghans feeling less secure, said Western and Afghan officials.

President Hamid Karzai quickly expressed his condolences in a strong statement that reminded the French of their long involvement with Afghanistan and conveyed the Afghan people’s gratitude.

“Throughout history, the two countries have enjoyed a sincere relationship, which Afghan people will always cherish,” Mr. Karzai said.

The four French service members were killed and a number more wounded on Friday when a gunman wearing an Afghan National Army uniform turned his weapon on them, according to an Afghan police official in Kapisa Province in eastern Afghanistan where the episode occurred and a Western official in Kabul, who spoke on condition of anonymity because he was not authorized to speak to the press. The Afghan police official, Asadullah Hamidi, said the shooting happened in the southern part of Tagab District, an area that is viewed as dangerous and dominated by insurgent forces.