A French intelligence agent, Denis Allex, was killed on Saturday when an operation to free him from Al Shabaab militants holding him hostage in Somalia failed.
Two French commandos are also feared dead, France 24 reported, citing the Defense Ministry.
Troops swooped in via helicopters on the town of Bulo Marer, in southern Somalia, late last night, hours after France announced that it would launch a military operation against Islamists in Mali.
"Intense combat" followed, Defense Minister Jean-Yves Le Drian told reporters in Paris, during which the government believes Allex was killed by his captors, one commando died and another was left missing. Some 17 militants died.
Al Shabaab, however, released a statement claiming that Allex was alive and in a different location. Their spokesman said that his fate would be announced "within two days."
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The rescue mission was not part of the Mali intervention, Le Drian said, but Reuters notes that the French government must have been aware its actions there could have dangerous consequences for the hostages being held by Islamists elsewhere in Africa.
Eight other French citizens are currently in captivity around the Sahara region, according to Reuters.
According to France 24, Allex was in Somalia to train government forces for the fight against Islamist insurgents when he was kidnapped from Mogadishu in July 2009.
At least two videos have since been released purporting to show Allex asking the French government to stop supporting the Somali government and negotiate his release, most recently in October 2012, the BBC said.
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