An Afghan soldier has shot dead five of his fellow troops at a coalition base in southern Helmand province, Afghan and US authorities say.
Six others were wounded before he was shot and killed. The reason for the incident is unclear.
"No information is available as to his motives," a statement issued by the US military said.
About 18,000 US-led coalition forces are in Afghanistan hunting Taleban and al-Qaeda militants.
Elsewhere in Helmand province, Afghan officials said troops killed two local militia leaders in clashes on Wednesday.
Coalition troops not wounded
The soldier who began the shooting had just come off guard duty at the base.
"No evidence indicates this attack was conducted by any anti-coalition militia forces," the US military statement said.
No coalition soldiers had been wounded in the attack, it added.
" We do not know the cause of this clash at this stage "
Those wounded have been taken to a US military hospital in the southern city of Kandahar.
An Afghan defence ministry spokesman said the cause of the clash was not known.
"We do not know at this stage what happened and what went wrong," Gen Zahir Azimi told Reuters news agency.
US-led coalition troops operate alongside the fledgling Afghan national army, which currently has under 20,000 soldiers. It plans to recruit and train 70,000.
The army will be largely paid for by the US and UK governments.
The Afghan government is also working to create a national police force, for which Germany is helping to train officers.
Afghanistan is recovering from years of war and militants and private militias hold sway in large areas of the country.
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