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"A man wearing Afghan army uniform opened fire on French nationals killing four and injuring 16 others this morning in Tagab district of Kapisa province," a security official told AFP on condition of anonymity.
A spokesman for NATO forces said four NATO troops were killed and the shooter had been arrested, but did not give the nationality of the troops.
"Four International Security Assistance Force service members were killed today in eastern Afghanistan by a member of the Afghan National Army," the US-led force said in a statement.
French troops had surrounded their base in Kapisa and were not allowing any Afghan soldiers to approach, a security source told AFP.