Bono said the attack "could have been an accident or it could have been an attack from the exterior."
"We believe it is best not to rule out that it could have been an accident caused by technical reasons, nor can we rule out that it could have been an external attack," Bono said.
A spokesman for the International Security Assistance Force (ISAF) in Kabul said that a second Spanish helicopter also made an emergency landing.
Spokesman Major Andrew Elmes said the cause of the crash and the emergency landing were still unknown. Both incidents took place south of Herat.
Some reports said the two helicopters collided in bad weather.
(Reuters/AFP/AP)
See also
17 Spanish Troops Killed In Afghan Helicopter Crash
For weekly news and analysis on Afghanistan, subscribe to "RFE/RL Afghanistan Report."
"We believe it is best not to rule out that it could have been an accident caused by technical reasons, nor can we rule out that it could have been an external attack," Bono said.
A spokesman for the International Security Assistance Force (ISAF) in Kabul said that a second Spanish helicopter also made an emergency landing.
Spokesman Major Andrew Elmes said the cause of the crash and the emergency landing were still unknown. Both incidents took place south of Herat.
Some reports said the two helicopters collided in bad weather.
(Reuters/AFP/AP)
See also
17 Spanish Troops Killed In Afghan Helicopter Crash
For weekly news and analysis on Afghanistan, subscribe to "RFE/RL Afghanistan Report."