Afghanistan's government has promised to tighten up vetting of its police and army to cut down on a devastating rash of insider attacks on foreign forces, although it blamed foreign spy agencies for the majority of the killings.

This year, such shootings have killed some 40 people, accounting for around 10% of all Nato deaths in Afghanistan. They are a mounting political liability in Washington and have already contributed to France's decision to bring its troops home early.

In a sign of growing concern, the Afghan president, Hamid Karzai, called in his security council to discuss the problem on a national holiday. It was just a couple of days after his US counterpart, Barack Obama, warned: "We have got to make sure we are on top of this" – although Karzai's spokesman denied any sense of coercion.

"We are not worried about the pressure from the international community," said spokesman Aimal Faizi. "We know that this is an important issue for our international partners, but it is our own concern as well because we want to have a strong army and a strong police force.

"Reports presented by security officials in this meeting blamed the infiltration by foreign spy agencies into Afghan security force ranks as responsible for the rise in the shootings," Faizi told journalists after the meeting. "Neighbouring countries included," he added.

While he declined to give names, there is deep resentment in Afghanistan at interference by Iran, and also Pakistan, which provides safe haven to many insurgents just inside a shared border.

But while western diplomats and officers may welcome the government's decision to deal with the shootings, the fact it is pointing a finger across Afghanistan's borders and alleging that sophisticated infiltration is behind the majority of attacks is a direct challenge to Nato's stance that most have been the result of personal grudges turned violent.

Nato has long argued that most attacks – perhaps as many as 90% – are due to personal disputes gone wrong on military bases where weapons are easily to hand.

Faizi acknowledged the role of personal and cultural friction and highlighted the impact of Afghan outrage at the accidental burning of copies of the Qur'an on an major airbase, and series of incidents in which US soldiers were photographed desecrating corpses.

But he said the Afghan security forces would not be swayed by Nato's judgements. "That is the result of Nato's investigation, but we are talking about an investigation done and conducted by the Afghan authorities."

He said the meeting agreed proposals to try to stem the killings with a range of tighter security measures, ranging from stricter checks on the backgrounds of new recruits, and for current forces a biometric database of all police and army personnel, as well as more cultural training.

Details still need to be hammered out, but the extra vetting will be made possible in part by a slowdown of recruitment as Afghanistan gets close to its target police and army size after a rapid build up of forces. Recruitment has fallen from between 10,000 and 15,000 people each month to around 4,000 to 5,000 each month, Faizi said.

The Nato-led coalition declined to comment on the new measures or allegation of cross-border infiltration.