An Afghan army soldier killed two NATO troops in a new "green-on-blue" insider attack Monday, the US-led International Security Assistance Force said.

"A member of the Afghan National Army turned his weapon on ISAF forces, killing two ISAF service members in (eastern) Laghman province today," a spokesman told AFP.

"ISAF soldiers returned fire and killed the attacker."

The latest deaths take the toll from insider attacks this month alone to 12 and to a total of 42 this year, making up around 13 percent of all NATO deaths in 2012.

NATO has struggled to stem the attacks in which uniformed Afghans turn their weapons against their international allies and they have become a major issue in the Afghan war, eroding trust between the two forces.

Taliban insurgents claim responsibility for many of the attacks, but NATO attributes most to cultural differences, stress and personal animosity between Afghan troops and their international allies.

The commander of NATO forces in Afghanistan acknowledged last week, however, that the Taliban may be responsible for a greater share of insider attacks than previously claimed by the Pentagon.

US General John Allen told reporters that about 25 percent of all such attacks were the result of the Taliban infiltrating Afghan forces, after the Pentagon had said the Taliban were responsible for only about 10 percent.

Allen said the attacks were caused by various factors, including "disagreements, animosity which may have grown between the individual shooter and our forces in general, or a particular grievance".

He said that the recent spate of assaults may have been related to the Muslim holy month of Ramadan, as Afghan soldiers were under strain from fasting in intense heat while engaged in combat. But Ramadan ended last week.