KABUL: An Afghan in police uniform shot and killed a Nato soldier in southern Afghanistan Sunday, the military said -- taking the death toll from insider attacks this year to 40.



"An International Security Assistance Force service member died when an individual wearing an Afghan Uniformed Police uniform turned his weapon against ISAF service members in southern Afghanistan today," Isaf said.



Afghan and Isaf officials were investigating the incident, a statement said without giving further details or specifying the soldier's nationality.



A spike in so-called green-on-blue attacks is causing growing concern in the United States and among its Nato allies fighting the Taliban insurgency in Afghanistan.



The latest death takes the toll among international coalition soldiers from such incidents to 10 in less than two weeks, sharply eroding trust between foreign troops and the Afghans they work with.



Two American soldiers were killed last Friday, a week after six were killed in a single day on August 10. Another Nato soldier was killed three days earlier.



Some of the attacks are claimed by the Taliban, who say they have infiltrated the ranks of Afghan security forces, but many are attributed to cultural differences and antagonism between local and US-led allied forces.



In a sign of US concern, Pentagon chief Leon Panetta called Afghan President Hamid Karzai on Saturday, urging him to crack down on the attacks.



The pair "agreed that American and Afghan officials should work even more closely together to minimise the potential for insider attacks in the future", the Pentagon said.



Measures should include improved intelligence and more rigorous vetting of Afghan recruits, a statement said.



The growing number of attacks will likely add to pressure in Nato nations for an exit as soon as possible from the increasingly unpopular war, now nearly 11 years old.