NATO says it is investigating whether an Afghan National Army soldier has killed several coalition service members in southern Afghanistan.
NATO says it is conducting the probe with the Afghan government to determine how the alliance troops died Friday on a military base in Sangin in Helmand province.
The Taliban says an Afghan solider shot and killed at least two NATO service members and then defected to the insurgency.
NATO troops share bases with Afghan soldiers, leaving coalition forces vulnerable to attacks by infiltrators.
Meanwhile, Spain's prime minister, on a surprise visit to western Afghanistan, said Saturday that his country's troops are "not here to stay."
Jose Luis Rodriguez Zapatero told Spanish troops at Qala-i-Naw that Spain's commitment, however, will be firm until the Afghans can guarantee their own security. He said once that is achieved "we all will have gained a better world."
U.S. President Barack Obama wants to begin withdrawing U.S. troops from Afghanistan in July of next year, depending on the readiness of Afghan forces and other security factors.
In July, an Afghan soldier killed two U.S. contractors inside a military base in northern Afghanistan. A week later, another Afghan solider killed three British soldiers.
In 2009, five British soldiers were killed by an Afghan policeman.
Some information for this report was provided by AP, AFP and Reuters.