ASADABAD (AFP) - Children aged between seven and nine were killed in a Nato airstrike in northeast Afghanistan when foreign forces mistook them for insurgents, a police chief said Wednesday. The claim came after the Nato-led International Security Assistance Force (Isaf) said late Tuesday it was probing claims of civilian casualties after its troops countered an attack on a base in Darah-Ye Pech district, Kunar province. The incident is the latest claim of civilian casualties in Kunar. Earlier this week, an official delegation appointed by Afghanistans government accused Nato-led forces of killing 65 civilians in recent operations there, although Isaf insists there was only a handful of civilian injuries. Yesterday in the morning, the coalition base came under rocket attack from nearby mountains, Khalilullah Ziayee, the police chief for the restive province, told AFP. At around noon, the forces identified the location from where the rockets were fired and responded with airstrikes. They hit children who had climbed the mountains to collect firewood. Nine children have been killed. He added: The children were aged between seven and nine. A spokesman for Isaf said it had no further information to add to the statement it issued Tuesday, in which it said it takes claims of civilian casualties very seriously would investigate quickly and thoroughly. Civilian casualties during international military operations against insurgents are a key cause of friction between the Kabul government and its Western supporters.