Kabul, Afghanistan (CNN) -- A soldier in the Afghan National Army uniform shot dead two French soldiers serving in eastern Afghanistan on Thursday, the French Defense Ministry said.
The soldiers were there as part of NATO's International Security Assistance Force.
French Defense Minister Gerard Longuet said the two French soldiers had been deliberately fired on by an Afghan soldier present at their position in the Kapisa valley.
He condemned the attack as a "cowardly act" but reaffirmed France's commitment to helping the Afghan National Army develop and its confidence in the Afghan soldiers.
The "isolated incident" would not affect the process of eventually handing over responsibility for security to Afghan forces, the minister said in a statement, adding that his thoughts were with the families of those killed and their fellow service members.
French President Nicolas Sarkozy said he had learned of the deaths of the two men, who served in an engineers' regiment, with great sadness.
"During a support mission for the Afghan National Army (ANA) in Tagab Valley, these two non-commissioned officers were fatally hit by the deliberate shooting of an Afghan soldier of the ANA," his statement said.
Sarkozy also reiterated his country's "determination to continue working within the International Security Assistance Force to restore peace and stability in that country and contribute to its development."
A text message from the Taliban about the same incident claimed three French soldiers had died: "An Afghan soldier killed three French soldiers in their base in Tagab district of Kapisa province on Thursday at 6 a.m. The Afghan soldier himself was also killed."
The latest deaths come two days after three service members were killed in a roadside bomb attack, also in eastern Afghanistan, the alliance said.
The Taliban also claimed responsibility for the attack on Tuesday.
The latest deaths bring the number of service members killed in Afghanistan this year to 553, according to a CNN count.
Last year, 711 service members died.
CNN's Laura Smith-Spark and Pierre Meilhan contributed to this report.