A military probe has cleared Canadian soldiers in the fatal shooting of an Afghan policeman, concluding his vehicle was unmarked when it sped towards a checkpoint.

The officer died in late August, after soldiers opened fire on his white pickup truck, about 25 kilometres west of Kandahar.

One bullet passed through the vehicle's windshield, killing the officer. Six other Afghan police officers were injured.

Some witness accounts claimed the truck was marked as an Afghan police vehicle. But the Canadian Forces National Investigation Service (NIS) has released a photograph of the vehicle, clearly showing it was unmarked.

NATO had remained adamant the soldiers could not have known they were firing at police officers.

"Neither their vehicle, nor their immediate appearance, readily identified them (as police)," Col. Fred Lewis, the deputy commander of Canada's NATO contingent in southern Afghanistan, said in August.

NIS also concluded soldiers correctly followed the necessary rules of engagement. Some witness accounts said the police had shot at the soldiers, who then returned fire.

The dead officer is believed to have been a part of Afghanistan's secret police.