The Afghan Taliban said on Saturday they had recruited an Afghan soldier who shot dead four French soldiers a day earlier, raising fears the militant group had managed to deepen its infiltration of the country's struggling security forces.
The killings prompted France to threaten an early pullout from the Nato-led war.
The claim of responsibility raises serious concerns about handing control of security over to the Afghan army and police, which Nato-led forces are currently in the process of doing before all foreign combat troops leave by the end of 2014.
"The Emirate of Afghanistan has recruited people in important positions," Taliban spokesman Zabihullah Mujahid told Reuters by telephone from an undisclosed location, using another name the militant group call themselves.
"Some of them have already accomplished their missions."
The four French soldiers died on the spot, he said.
The killings in Kapisa province were the latest in a string of such attacks in which Afghan troops turn on their Western allies and mentors. While Nato has blamed Taliban infiltration in the past, it has also said stress, indiscipline and divided loyalties within the hastily trained ranks played a role.
Such attacks are especially damaging as the Afghan National Army tries to win public trust before foreign troops leave.
The Taliban claim coincided with a visit to Kabul by the US Special Representative to Afghanistan and Pakistan, Marc Grossman. He is expected to meet President Hamid Karzai and other senior Afghan officials.
Despite the presence of more than 100,000 foreign troops, violence across Afghanistan remains at its worst levels since the Taliban were toppled by U.S.-backed Afghan forces in late 2001, according to the United Nations.
In April last year, an Afghan Air Force pilot opened fire at the military wing of Kabul's main airport, killing eight US troops and an American contractor.
An Afghan border policeman shot dead six US soldiers during a training mission in Nangarhar province in 2010.
US and Nato officials usually describe such attacks as isolated incidents.
Afzal Aman, head of operations for the Afghan National Army, said he could not confirm if the Taliban had infiltrated the army in this instance. But he suggested that such recruitment could represent a bigger threat than previously thought.
"Usually in the past, whenever something like this happened, it came about after Afghan and foreign soldiers had an argument over something related to Afghan affairs," he told Reuters.
Friday's attack also comes weeks after an offer from the Taliban to open a political office in Qatar as a prelude to possible peace talks with the United States and other nations.
After the shooting -- which took the French death toll to 82 since the war began in 2001 -- President Nicolas Sarkozy ordered all French military operations on the ground to be suspended and Defence Minister Gerard Longuet jetted into Kabul on Saturday.
A regional Taliban commander added that incidents such as a video showing US Marines urinating on corpses were boosting support for the group among Afghans and threatened more attacks.
"Our missions have become easier because of incidents like the video," he said.