The US says it is suspending training for some new Afghan security force recruits while checks are carried out on possible ties to the Taliban.
A US spokesman told AP it would affect 1,000 local police trainees.
The move follows a series of incidents in which foreign troops have been killed by Afghan soldiers or policemen.
Military guidelines have sometimes not been followed for fear of slowing the growth of the Afghan security forces, officials told the Washington Post.
US Special Operations Forces spokesman Lt Col John Harrell said training had been put on hold for one to two months to review any potential ties recruits might have to insurgents.
Operations by forces already trained would continue, as would the recruitment of new trainees, he said, according to Associated Press.
On Wednesday, three Australian soldiers were killed by a man in Afghan army uniform in Uruzgan province.
Currently, approximately 130,000 Nato troops are fighting insurgents in Afghanistan alongside 350,000 Afghans.
Some 45 coalition troops have died in more than 30 "green-on-blue" attacks this year.
The term refers to the colour-coding systems used by the US military - Nato forces are "blue" and Afghans are "green".
The Taliban has been actively recruiting members of the Afghan security forces, publicly announcing that insider attacks were a central part of their strategy against Nato forces.
Most of the victims of the green-on-blue attacks have been Americans.
