Afghan official says NATO helicopter strike kills 4 civilians; NATO says it is investigating

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An Afghan official says a NATO helicopter strike has killed four civilians in the country's west. Officials with the international military coalition say they are investigating the attack.

The attack saw almost 200 people protest against NATO in Herat province on Tuesday.

Raouf Ahmadi, a spokesman for the chief of police in Herat province, says the attack happened Monday in the province's Shindan district after Taliban fighters apparently launched a missile. Ahmadi says the NATO helicopter responded with fire that killed four civilians.

In a statement, NATO said it was aware of the attack and was investigating, without elaborating.

Casualties from NATO strikes remain a contentious issue in Afghanistan as international troops prepare to withdraw from the country at the end of this year.