The NATO force in Afghanistan says insurgents are not responsible for most of the attacks by Afghan security force members on their NATO colleagues. The coalition instead blames personal grievances and battle stress suffered by Afghan troops.

NATO spokesman Brigadier General Carsten Jacobson said Monday that investigators have found “signs and symptoms” that could have been seen in those cases. He said leadership must improve to make sure that those signs are identified before an incident happens.

So far this year, NATO says Afghan security personnel have shot dead 17 foreign troops in 10 separate so-called “green-on-blue” incidents. The Taliban normally claims responsibility for the violence.

In the wake of the attacks, NATO officials say they are implementing enhanced security measures.

Meanwhile, officials in northern Afghanistan say twin bomb blasts wounded at least 23 people at a market in Baghlan province Monday morning.

A medical official said the casualties include children, students and police officers. At least seven Afghan security force members also were wounded.

There was no immediate claim of responsibility.