The top US military officer held talks with Nato commanders in Afghanistan on Monday, looking to halt unprecedented attacks by Afghan allies that have killed 40 Western soldiers so far this year.
Ten soldiers, mostly Americans, have been killed by Afghan allies in the past two weeks, while the total toll of 40 this year makes up 13 percent of all international coalition deaths.
Mistrust spawned by the so-called green-on-blue assaults has reached the stage where foreign troops have been ordered to be armed at all times, even within bases, a Nato spokesman told AFP.
The attacks -- on a scale believed to be unprecedented in modern military history -- are responsible for almost one in every four coalition deaths in the war so far this month.
In the latest incident an Afghan in police uniform killed a Nato soldier in the south on Sunday, shortly before General Martin Dempsey arrived, the military said.
Dempsey, chairman of the US Joint Chiefs of Staff, told reporters at Bagram airbase the rise in the number of attacks would be a key focus of his meetings with US-led coalition and Afghan officers.
Despite expanded efforts to screen recruits and preempt potential turncoat attacks, Dempsey said the number of incidents continues to increase.
"We have an eight-step vetting process that's been in place in earnest for about a year. But we haven't turned the corner on the trend," he said.
Some of the attacks are claimed by the Taliban, who say they have infiltrated the ranks of Afghan security forces, but in the past Nato has attributed many to cultural differences and antagonism between local and US-led allied forces.
Dempsey suggested the Afghan government could do more to thwart the attacks, including more lower-level officials speaking out on the problem.
"I do think the more they can be as concerned about it as we are, the better off we'll all be," he said.
In another a sign of US concern, Defense Secretary Leon Panetta urged Afghan President Hamid Karzai at the weekend to bolster cooperation with ISAF forces to contain the threat.
Measures should include improved intelligence and more rigorous vetting of Afghan recruits, a Pentagon statement said.
Nato has about 130,000 soldiers fighting an insurgency by Taliban, but they are due to pull out in 2014 and work increasingly with the Afghans they are training to take over.
Dempsey said the insider violence would not alter the timetable for withdrawal.
But the growing number of attacks is likely to add to pressure in Nato nations for an exit as soon as possible from the increasingly unpopular conflict, now nearly 11 years old and America's longest war.
New Zealand pledged Monday to withdraw from Afghanistan as quickly as possible after three of its troops were killed, albeit in a bomb attack, not at the hands of their Afghan colleagues.
Western military officers and politicians are grappling with how to curb the attacks by presumed allies, which are on a scale unknown in recent wars such as those in Vietnam and Iraq, experts say.
"To the best of my knowledge the sort of 'green on blue' attacks on the Western troops in Afghanistan have no parallel in recent military history," Nick Mills, an associate professor of journalism at Boston University who served the US Army as a photographer in Vietnam told AFP.
"The Afghans know that once the Western troops leave, they are going to have to choose sides -- the Kabul government or the Taliban -- and the Kabul government has little respect or credibility.
"The average Afghan, I think, does not believe the Kabul government has the strength to protect him once the Western forces pull out," Mills said.