The French troops were shocked to discover not only two hostages in their captors' lair, but two other foreign women whom nobody knew had been kidnapped.
In the early hours of Friday morning, French commanders launched an operation to rescue two French tourists held captive in the Burkina Faso region.
Following the kidnappers in a remote shelter, the French troops have moved.
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Despite careful planning and American and Burkina support, "no one had any knowledge" of the presence of a French and South Korean defense minister, Florence Parly, at a press conference.
Four "terrorists" were also killed during the previous operation at dawn.
The contacts with the United States and South Korea "show that these countries probably were not aware of the presence of their two citizens on the territory of Burkina Faso," he added.
Parly said the four freed hostages were in a "safe place". The French president, Emmanuel Macron, plans to welcome the home of French citizens and South Korean citizen to the military airport of Paris on Saturday night.
The American woman had to be repatriated separately.
Both hostages, French music teachers Laurent Lassimouillas and Patrick Picque, disappeared 11 days ago while they were on safari in the remote Pendjari National Park, in northern Benin.
Their disappearance became apparent when they failed to return from sightseeing.
The disfigured body of their guide was subsequently found, along with their abandoned vehicle.
Little is known about the South Korean and American hostages, who apparently were in the hands of the kidnappers for 28 days.
Two agents of the French special forces, Cedric de Pierrepont and Alain Bertoncello, tragically lost their lives during the rescue mission.
In a statement on Friday, Macron expressed condolences for the death of the two marines who participated in the French operation Barkhane, who worked to eradicate the terrorists who roam the Sahel region.
Reportedly, the two soldiers were killed closely as they entered one of the four kidnappers' shelters.
In a statement obtained by the BBC, Macron said that "he bows with emotion and solemnity before the sacrifice of our two soldiers who gave their lives to save those of our citizens".
A military ceremony for the commanders is scheduled for next week.
Macron thanked the authorities of Burkina Faso and Benin for their cooperation and promised them support in the fight against terrorism.
During the operation, four kidnappers were also killed, while two others fled.
Ms Parly said that the identity of the kidnappers was not yet known, but there were two main militant groups operating near where the French tourists had been taken, one connected to al-Qaeda and the Other to the Islamic State group.
The chief of staff of the army, General Francois Lecointre, said that the hostages and their captors were in transit in Burkina Faso "with the intention of the kidnappers to take them to Mali".
"Once the hostages were in their hands it would have been impossible to save them," the general told reporters.
Islamic extremists have become increasingly active in Burkina Faso, raising concerns that militants could also infiltrate northern Benin and neighboring Togo.
France has 4,500 soldiers in a military force in the Sahel in order to help local governments fight Islamic extremists.
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