LOS LLANOS MILITARY BASE, Spain — Investigators were probing Tuesday how a fighter jet crashed during elite NATO training exercises at an air force base in Spain, killing 11 military personnel and 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 on Monday.

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

Several bodies were still lying on the tarmac a day later and could not be safely moved until emergency teams clean up toxic fuel spilled in the crash, Spanish air force spokesman Jose Guerreira told reporters.

Two Greek pilots on board and eight French officers on the ground were confirmed killed on Monday and Spanish defence ministry said a ninth French victim died in a hospital burns unit in Madrid on Tuesday.

The dead included one Frenchwoman, a captain, the French defence ministry said.

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

Nine French personnel and up to 12 Italians were injured, officials from both countries said.

The jet — involved in an elite training program — crashed after losing power as it took off, the Spanish defence ministry said, damaging two Italian planes and three French jets.

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

French prosecutors also launched inquiries and French accident investigators were at the base, officials said.

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

'Tragedy for NATO'

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

Flags flew at half-mast at Nancy-Ochey air base in eastern France, where seven of those killed were from. Both houses of the French parliament held a minute's silence.

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.

French Defence Minister Jean-Yves Le Drian arrived at the site of the accident on Tuesday.

The new prime minister of Greece, Alexis Tsipras, sent the head of the chiefs of staff Evangelos Tournas to the base, state media reported.

NATO Secretary General Jens Stoltenberg called it "a tragedy which affects the whole NATO family," 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 program are Belgium, Britain, Denmark, France, Germany, Greece, Italy, the Netherlands, Spain and the United States.

The plane that crashed was taking part in NATO's Tactical Leadership Programme, which seeks to improve multinational cooperation in air operations.

According to the French defence ministry's website, it is "the most renowned and most demanding" program for fighter pilots.

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.

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