Every few days

As readers are no doubt aware, incidents involving NATO or coalition forces killing civilians occur with distressing frequency - on average about one every three or four days. This time, the incident was in Kandahar province, where Canadian troops are in charge:

Security developments in Afghanistan

Feb 17, KANDAHAR (Reuters) - NATO-led troops shot dead two Afghan civilians in a vehicle which sped towards a foot patrol and failed to stop after warning shots were fired in Maiwand district [Kandahar province], 400 km (250 miles) southwest of Kabul, the NATO-led force said. (link)

February's toll:

February 5-6: US-led coalition forces in Zabul kill 6 civilians in an attack which targeted insurgents, say Afghan officials.
February 6: US-led coalition forces shoot and kill one man and wound a woman and child at a checkpoint in Khost province.
February 11: A provincial spokesman says NATO airstrikes kill four civilians in Logar province.
February 12: Five children are killed as Australian special forces battle militants while searching a house in Uruzgan province.
February 17: Two civilians in a vehicle are killed by NATO-led troops on patrol in the Maywand district of Kandahar.