Ten people have died in a fighter jet crash at a military base in Spain, the Defence Ministry says.
Military officials said that the Greek F-16 jet crashed into other planes and exploded at the Los Llanos airbase in Albacete in central Spain.
One of the pilots performed a wrong manoeuvre during take-off, according to local media. Both pilots were killed.
Another 13 people have been injured, six of them seriously, according to officials.
The crash sent flames and a plume of black smoke billowing into the air. Most of the victims are not believed to be Spanish, officials say.
Emergency crews are working to extinguish the blaze and find out how much damage has been done to other planes involved in the Nato exercise, the ministry said in a statement.
Nato Secretary General Jens Stoltenberg said that he was deeply saddened by the crash.
"This is a tragedy which affects the whole Nato family," he said. "I express my heartfelt condolences to the loved ones and the nations of those who lost their lives, and I wish a speedy recovery to the injured."
A Nato spokeswoman talking to the AP news agency declined to reveal details of the accident.
Spanish officials said that the jet was participating in a Nato training exercise called the Tactical Leadership Programme (TLP).
The TLP is not part of the Nato structure but is an organisation formed under an agreement between 10 Nato nations whose aim is to increase the effectiveness of allied air forces through the development of leadership skills.