Patrick Hennessey, a soldier and author, has described the tension between Afghan and British soldiers as an "increasing problem", after an Afghan soldier shot dead three Australian soldiers inside a military base last week.
One in seven of all Nato deaths this year in Afghanistan has been caused by Afghan troops or police.
Speaking to the Today programme on BBC Radio 4, Mr Hennessey said that serious cultural differences need to be addressed. He added that some Afghan soldiers he spoke to recently felt they were being abandoned.
He said: "They're seeing their British and American mentors going home ever six months or every twelve months, and they're thinking: 'We're still here'."
Mr Hennessey's latest book, Kandak: Fighting With The Afghans, is a portrait of the Afghan army.
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