Two American soldiers have died in another apparent insider attack in Afghanistan.
A man wearing an Afghan police uniform fired on US troops in Khas Uruzgan in central Uruzgan province, NATO's International Security Assistance Force (ISAF) said in a statement.
The incident is being investigated, ISAF said, without giving further details.
The attacker escaped and it is not yet known whether he was genuinely a police officer or was wearing a disguise, a spokeswoman for US forces in Afghanistan told the Associated Press.
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At least 54 coalition troops have been killed this year in so-called "green-on-blue" attacks, according to Reuters.
Just yesterday, two British service members died in a gunfight in Helmand province with an Afghan man believed to have been a police officer, though he was not in uniform at the time, the BBC reported. He was also killed.
Around a quarter of insider attacks are blamed on Taliban insurgents who have infiltrated the Afghan security forces, but most are blamed on disputes between coalition forces and their Afghan allies, according to Agence France-Presse.
NATO forces have introduced new precautions to prevent such incidents, including re-vetting police recruits, banning joint patrols between Afghan and foreign troops and ordering soldiers to carry their weapons at all times.
Meanwhile the Afghan Defense Ministry has drawn up "cultural guidelines" for its forces, AFP says, which instruct Afghan soldiers not to take offense if their NATO colleagues do things like exit the shower naked, swear or ask to see pictures of their wives.
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