Officials investigated Tuesday how a fighter jet crashed during NATO training exercises at an air force base in Spain, killing 11 military personnel leaving others with serious burns.

Nine French and two Greek personnel died and about 20 people were injured after the two-seater F-16 crashed into parked aircraft at the Los Llanos base in southeastern Spain.

The jet lost power as it took off and crashed on Monday, damaging five other aircraft, the Spanish defence ministry said.

Firefighters rushed to the scene and battled the flames as black smoke billowed from the wreckage.

Two Greek pilots on board and eight French officers were confirmed killed on Monday and the ministry said a ninth Frenchman died in hospital in Madrid on Tuesday.

A judge in the eastern city of Valencia was leading an investigation of the accident.

A technical commission was also probing the causes and was set to examine the wreckage and the plane’s black box recorders, a defence ministry source said.

The base, near the city of Albacete, hosts elite exercises run by NATO to train military personnel from 10 nations to carry out joint manoeuvres.

Two pilots, a navigator and five mechanics were among the French personnel killed, the head of the French air force chiefs of staff Denis Mercier told BFM television.

Nine French personnel and 11 Italians were injured, Spanish officials said.

It was the highest death toll in a single day for the French armed forces since an ambush in Afghanistan in which 10 died in 2008.

Of those injured, five of the French were in “serious but stable condition” in hospital and four had been discharged, said defence ministry spokesman Manuel Vazquez.

French President Francois Hollande “expressed his deep respect for the commitment” of the airmen who were preparing for air force missions to fight “against terrorist groups” in Iraq and the African Sahel region.

Spain’s Defence Minister Pedro Morenes and the chief of staff of Spain’s air force, Francisco Javier Garcia Arnaiz, arrived late Monday at the airbase, about 250 kilometres (150 miles) southeast of Madrid.

French Defence Minister Jean-Yves Le Drian was expected to visit the site of the accident on Tuesday.

– ‘Tragedy for NATO family’ –

The Greek F-16 hit two Italian AMX planes and three French jets — a Mirage 2000 and two Alfa Jets — when it crashed.

It was taking part in NATO’s Tactical Leadership Programme, which seeks to improve multinational cooperation in air operations.

NATO Secretary General Jens Stoltenberg said he was “deeply saddened” by the disaster.

“This is a tragedy which affects the whole NATO family. 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,” he said in a statement.

Britain, Germany, the United States and Spain were also taking part in the exercises but none of their nationals were reported injured.

The 10 NATO countries that take part in the programme are Belgium, Britain, Denmark, France, Germany, Greece, Italy, the Netherlands, Spain and the United States.

According to the French defence ministry’s website, it is “the most renowned and most demanding” programme for fighter pilots.

The base has housed the training centre for NATO pilots since 2010, according to its website.

Some 750 personnel were taking part in the current course.

The F-16, manufactured by US company Lockheed Martin, is the biggest-selling fighter plane in the world with more than 4,500 made for 28 countries.