Spokesman George Little said Panetta encouraged Karzai to work with U.S. commanders to ensure more rigorous vetting of Afghan recruits. Little said Panetta and Karzai agreed that American and Afghan officials need to work together to address a problem that has intensified in recent days.
In the latest incident, an Afghan police officer on Friday shot to death two U.S. servicemen during a training exercise in the western province of Farah.
Little said Panetta advised more effective counterintelligence measures to identify potential attackers from inside the ranks of Afghan security forces, as well as "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."
The phone call was a sign of growing concern in Washington about the insider threat, particularly because American and allied troops are now working more closely with the Afghan army and police in preparation for the transition to complete Afghan security control by 2014.
On Friday it was disclosed that U.S. troops have been ordered to carry loaded weapons at all times in Afghanistan, even when they are on their bases. The order was a precaution against insider attacks.