Four soldiers fighting with the Nato-led alliance were killed in an attack believed to involve members of the Afghan police in southern Afghanistan on Sunday, the coalition said.
The incident came a day after two British soldiers were shot dead by an Afghan policeman while they were returning from a patrol in southern Helmand province, one of the strongholds of the Taliban-led insurgency.
At least 51 foreign military personnel have been killed in "insider" attacks this year, attacks which have put a heavy strain on trust between the coalition and Afghanistan as they move towards handing security responsibility to Afghan forces by the end of 2014.
The spike in such attacks has led to the training of new recruits to the Afghan army and police being suspended.
With foreign combat troops withdrawing from the increasingly unpopular and expensive war by the end of 2014, the enormous cultural divide that still separates Afghans and their allies after 11 years of war has become more of a concern than ever.
The Nato-led coalition and their Afghan counterparts have created a special Joint Casualties Assessment Team to investigate every attack.
In more than half of cases, attackers are either killed or escape and the motive for the incident never emerges, making it more difficult for the coalition to stem the surge in incidents.
There have been at least 37 insider attacks so far this year.