Three civilian contractors were killed by a gunman wearing an Afghan national security force uniform on Sunday.
Meanwhile, a further five NATO troops were been killed in roadside bombings in Afghanistan over the past two days, the Associated Press reported.
The artillery shells hit homes along frontier areas from which insurgents have in the past staged cross-border attacks.
According to Reuters, the latest rogue shooting by an Afghan occurred at a regional training center in the relatively peaceful western province near Afghanistan's border with Iran.
"An individual wearing an Afghan National Security Force uniform turned his weapon against ISAF contracted civilian employees in western Afghanistan today, killing three," a spokesman for the NATO-led coalition said.
An unknown number of other people had been wounded, he said.
"Also, one insurgent was killed in the engagement and we are still looking for one more shooter."
All five of the NATO service members, meantime, were killed in roadside bomb attacks — one on Saturday and four on Sunday.
The deaths bring the number of foreign forces killed in July to 32, and the total for this year to 247 so far, the AP reported.
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