Afghan officials say they have detained or expelled hundreds of Afghan soldiers as part of a probe into a deadly string of insider attacks.
At least 45 international troops have been killed this year after Afghan security forces turned their weapons on their coalition counterparts.
Afghan Defense Ministry spokesman General Zahir Azimi said Wednesday the Afghan military has taken steps to prevent such attacks and has arrested or expelled hundreds of "suspicious" army soldiers as part of an ongoing probe that began about six months ago.
Azimi said many of the troops had been discharged for not having proper documents.
In a phone conversation Wednesday, NATO Secretary-General Anders Fogh Rasmussen told Afghan President Hamid Karzai he has deep concerns about the surge in insider attacks on coalition troops.
NATO spokeswoman Carmen Romero said Mr. Rasmussen also reaffirmed the coalition's commitment to the mission in Afghanistan.
In other news, NATO says two coalition personnel died in a helicopter crash in eastern Afghanistan. The cause of the crash is under investigation.
On Sunday, the U.S. military announced it was temporarily halting the training of 1,000 members of the Afghan Local Police in order to improve vetting procedures. NATO, which is responsible for training Afghan National Army and Afghan National Police recruits, has not suspended its training.
NATO says many of the so-called "green on blue" attacks are due to personal grievances and arguments, with about 25 percent attributed to Taliban infiltration, impersonation or coercion. "Green on blue" refers to a color coding system used by the military.