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Isaf said a US soldier mistook the Pashto service journalist for an insurgent when troops responded to a militant attack in the town of Tarin Kowt in southern Uruzgan province.

Khpulwak was one of 19 people killed.

Nato launched an inquiry after initial reports that Khpulwak had been killed by insurgents were questioned.

The BBC said it recognised that Isaf had provided clarification, ending a period of uncertainty, but it would study the details of the findings on receiving the full report.

Director of BBC Global News Peter Horrocks said: "Ahmed Omed's death further highlights the great dangers facing journalists who put their lives on the line to provide vital news from around the world. It is essential that journalists are given the best possible protection whilst reporting in dangerous situations so that the world can hear their stories.

"Our thoughts are with Ahmed Omed's family and we will continue to do all we can to support them."

Isaf said Khpulwak's death was tragic and has expressed condolences to his family.

But it said it was confident its soldiers had complied with the laws of armed conflict and rules of engagement and acted reasonably under the circumstances.

Heavy fighting had broken out in Tarin Kowt's market following three suicide bombings.

Heavy machine guns, rocket-propelled grenades and assault rifles were used by both sides, witnesses said. Afghan government forces received air support from Nato.

The Taliban admitted carrying out the attacks but denied killing the reporter, accusing government forces of shooting him as they fought to regain control of the area.

Khpulwak reportedly sent his brother two text messages at the time. The first read: "I am hiding. Death has come." In the second, he wrote: "Pray for me if I die."

Khpulwak, who also worked for the Pajwak Afghan news agency, joined the BBC in 2008.

In September 2009, Nato soldiers rescued kidnapped UK journalist Stephen Farrell from the Taliban but his Afghan colleague, Sultan Munadi, a UK soldier and two Afghan civilians died in the operation.

And in October 2010, kidnapped UK aid worker Linda Norgrove was killed by a grenade thrown by a US special forces team as it tried to rescue her in Kunar province.

Isaf is the 140,000-strong, Nato-led force that is tackling the Taliban insurgency.

Although casualties are down slightly this year from 2010, there were 66 US combat deaths in August 2011, according to an unofficial tally by the Associated Press, making