(CBS News) KABUL, Afghanistan - In another example of increasing "green-on-blue" attacks, three British soldiers were killed in Helmand province on Sunday by a member of the Afghan security forces.
The man, a member of the Afghan Local Police force, was wearing his uniform when he shot the soldiers and has been taken into custody.
Afghan forces - or individuals wearing the uniforms of security forces - have killed 27 coalition soldiers already in 2012.
Last year, 35 members of the International Security Assistance Force-Afghanistan (ISAF) were officially listed as being killed by Afghan soldiers or police. The number of attacks, however, could be much higher, as ISAF doesn't release information about attacks where no coalition forces were killed.
To try and stop the attacks, "guardian angels" are now routinely used whenever coalition forces engage in a live fire exercise with their
Afghan counterparts. The "guardian angel" is an armed coalition soldier that stands back from the exercise to keep watch on the Afghan troops.
No group has taken responsibility for this latest shooting, although the Taliban often claim they have infiltrated the Afghan security forces and are carrying out these attacks. Despite those assertions, a recent Defense Department report maintains the attacks are not carried out by insurgents.
"Investigations have determined that a large majority of green-on-blue attacks are not attributable to insurgent infiltration of the ANSF (Afghan National Security Forces), but are due to isolated personal grievances against coalition personnel," the report says. "There is no indication that these recent attacks are part of a deliberate effort by insurgents, nor were they coordinated with each other."
The report goes on to say that recruiting polices for Afghan soldiers and police have been tightened in an effort to keep disgruntled Afghans from joining.
Whatever the reasons, the trend is especially troubling as the main mission for U.S. and coalition troops has now shifted to training their Afghan counterparts to take over security in the country.
Almost all operations and patrols are now conducted jointly by coalition and Afghan troops, with the hope that Afghan troops can soon take the lead, and let ISAF forces fall back into an advisory role.
New Afghan security approach sees U.S. forces scaling back: Click below for a full report}