A US soldier in camp in Afghanistan
The US says it is suspending training for new recruits to the Afghan local police (ALP) while checks are carried out on possible ties to the Taliban.
The move follows a series of incidents in which foreign troops have been killed by Afghan soldiers or policemen, reports the BBC.
The suspension of training - which only applies to new ALP recruits - will allow US special operations forces to "re-vet" current ALP forces.
US special forces currently have around 1,000 Afghan local police trainees.
"While we have full trust and confidence in our Afghan partners, we believe this is a necessary step to validate our vetting process and ensure the quality indicative of Afghan local police," Col Thomas Collins, spokesperson for US forces in Afghanistan, said in a statement.
The suspension of training would be "temporary", according to Col Collins, adding: "Despite the recent rise in insider attacks, they are relatively rare among SOF [Special Operations Forces]-partnered forces."
An existing eight-step vetting programme will be made more rigorous, officials say.
The number of counter-intelligence teams will be increased and there will be greater vetting when Afghan soldiers return from leave.
The sale of Afghan army and police uniforms will be made illegal.
Military guidelines on vetting have sometimes not been followed in the past for fear of slowing the growth of the Afghan security forces, officials told the Washington Post.
Operations by forces already trained would continue, as would the recruitment of new trainees, US Special Operations Forces spokesman Lt Col John Harrell told the Associated Press.
There are currently 16,380 members of the ALP.
The Afghan army and national police, trained by NATO, are unaffected by the suspension. The training of Afghan special forces will also continue.
On average, 7,000 Afghan soldiers and 3,700 Afghan police graduate from training every month.
The ALP is a relatively new force, introduced to improve security in some of the most remote parts of the country, the BBC's Quentin Sommerville in Kabul reports.
The force has been accused of human rights abuses, our correspondent adds.
Overnight it emerged that an ALP commander in Kunduz province had shot dead nine civilians and injured eight others, including women and children, with local media putting the death toll even higher.
One local media report suggested the attack was carried out in revenge for the killing of policemen by the Taliban.
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, at least 15 of them in August alone.