Kabul , Afghanistan ( CNN ) -- Another attacker in an Afghan police uniform killed a member of the NATO forces Sunday in Afghanistan , the latest in a slew of so-called `` green-on-blue '' attacks . The incident took place in southern Afghanistan , NATO 's International Security Assistance Force said . The attack brings to 40 the number of NATO troops killed in 32 such attacks this year , according to figures provided by ISAF . U.S. Secretary of Defense Leon Panetta urged Afghanistan on Saturday to take further steps to vet security force recruits . NATO : Most attacks on coalition troops driven by personal grievances . In a telephone call Saturday , Panetta encouraged President Hamid Karzai to work closely with the commander of NATO forces in Afghanistan to counter such attacks , Pentagon spokesman George Little said in a written statement . There were two green-on-blue attacks Friday . An Afghan police officer opened fire on U.S. troops in Farah province , killing two , the same day that an Afghan soldier wounded two NATO service members and an Afghan security force member in Kandahar province . Even as NATO blamed the majority of attacks on personal grievances rather than an infiltration by insurgents , ISAF commanding Gen. John Allen ordered all troops in the country to carry loaded weapons around the clock . Panetta urged Karzai to work closely with Allen to strengthen ISAF-Afghan cooperation to counter the threat , `` including augmented counterintelligence measures , even more rigorous vetting of Afghan recruits , and stepped up engagement with village elders , who often play a key role by vouching for Afghan security personnel , '' Little said . The attacks come at a critical time for the United States , which has picked up the pace of training Afghan forces as it prepares to withdraw troops by the end of 2014 . The telephone call between the two leaders came the same day a NATO airstrike killed a senior Taliban leader in the Kunar province , along Afghanistan 's northern border with Pakistan , ISAF said in a statement released Sunday . ISAF identified the man as Maulawi Nur Mohammad , whom it accused of planning and directing all Taliban activity in the Chapah Darah district . `` During the operation , the Afghan and coalition security force observed a large group of heavily armed insurgents engaging in insurgent activity , '' according to the release . `` After ensuring there were no civilians in the area , the security force engaged the insurgents with a precision airstrike . '' On Sunday , three ISAF service members were also killed in an improvised explosive device attack in eastern Afghanistan , ISAF said . Official : Man kills 3 US Marines at Afghan base . CNN 's Barbara Starr contributed to this report .
NEW : An attacker in an Afghan police uniform killed a NATO service member Sunday , Defense says . 3 ISAF troops were killed Saturday in an IED attack . Kandahar province Secretary of Defense Leon Panetta called Afghan President Leon Panetta on Sunday . NATO says an airstrike has killed a senior Taliban leader .