Another NATO soldier was killed on Sunday by an Afghan police officer, raising the coalition death toll from so-called "green on blue" shootings to nine in 11 days as the United States urged Kabul to step up screening of recruits.
The growing insider threat has eroded trust between NATO and its Afghan allies, causing a headache for Western powers who are planning to pull out most of their troops by the end of 2014.
US Defense Secretary Leon Panetta and Afghan President Hamid Karzai agreed to boost vetting of Afghan recruits to try to put an end to the spiraling attacks, now averaging one a week and far surpassing last year's toll.
Mr. Panetta also urged the president during a telephone call to work with NATO to boost counterintelligence efforts and speak more to village elders who have ties to the army and police, the Pentagon said in a statement.
"They expressed shared concern over this issue and agreed that American and Afghan officials should work even more closely together to minimise the potential" for future attacks, it added.
Two US special forces were shot dead on Friday by an Afghan militia member in western Farah province just as reclusive Afghan Taliban leader Mullah Mohammad Omar boasted that insurgents had successfully infiltrated security forces.
With Sunday's shooting, this year's death toll of NATO forces and contractors killed by their Afghan partners stands at 38 in 31 incidents compared to 35 dead in 21 attacks for all of 2011.
Bomb in 'safest province'
Adding to the carnage at the start of the three-day Eid festival ending Ramadan, three New Zealand soldiers were killed by an improvised bomb in northeast Bamiyan, thought to be the country's safest province until a string of recent attacks.
NATO's top commander in Afghanistan, US General John Allen, last week ordered all coalition forces to carry a loaded magazine in their weapons at all times on base after six Marines were killed on Aug. 10 in two separate insider shootings.
Field commanders have also been given discretion to increase numbers of so-called "guardian angel" sentries who oversee foreign soldiers in crowded areas such as gyms and food halls, to respond to any rogue shooting incidents.
"Commanders always have the ability to do whatever they think is right depending on their tactical situation," said a NATO official who spoke on condition of anonymity because of the sensitivity of security arrangements.
The attack on the New Zealand soldiers in rugged Bamiyan province, meanwhile, underscored the growing reach of insurgents in a area thought until recently to be largely safe.
Two other New Zealand soldiers were killed and six wounded on Aug. 5 in an insurgent attack blamed on a small band of hardcore militants said to have infiltrated the province to undermine security, targeting foreign and Afghan security forces. New Zealand has now lost 10 soldiers in Afghanistan.
Bamiyan was a focus of world attention in March 2001 when Afghanistan's former Taliban government destroyed two colossal sandstone Buddhas carved into cliffs, targeting the 1,700 year-old statues with tank and anti-aircraft guns, as well as dynamite, because they were un-Islamic.
The province, where most people belong to the Hazara ethnic group, opposed to the Pashtun-dominated Taliban, is in the Hindu Kush mountains around 150 miles northwest of Kabul.
Though infrequent bombings and sporadic attacks have taken place, the government had been working on making the province - home to the Band-e Amir chain of lakes - a center for tourism, with security provided by Afghan police and a small number of soldiers from New Zealand.
Bamiyan was one of the first provinces to be handed over to Afghan security forces in July 2011, with around 1,000 lightly armed Afghan police and intelligence forces based there, but no Afghan soldiers.