Two Frenchmen, one American, and one South Korean were abducted and taken to Burkina Faso, in West Africa.
French citizens Patrick Picque and Laurent Lassimouillas, both of them tourists, were visiting a wildlife preserve in Benin when they were abducted on May 1.
Their tour guide was fatally shot and their car was burned.
The South Korean and American hostages, both of them women, were held for 28 days. The US State Department did not release the American hostage's name due to privacy concerns but said she was in her 60s.
The French Foreign Ministry previously issued a travel guidance in the region.
It was unclear who the captors were, but terror organizations, like the Islamic State, have operated in the area.
The captors were believed to be handing the hostages off to an al-Qaeda group in Mali. The French Gen. François Lecointre told reporters it would have been "absolutely impossible" to successfully conduct a rescue operation under those circumstances.
Around 4,500 French troops are deployed to the region after the country set out to eliminate ISIS activity in Mali in 2013. Twenty-six French troops have been killed since the conflict.
The raid relied on intelligence from the US and France.
The original objective was to rescue the two French hostages.
French Defense Minister Florence Parly said that neither South Korea nor the US were "necessarily aware" of the abduction of their citizens, according to Reuters.
French officials, who were tracking the kidnappers, decided to strike after they set up a temporary camp.
"France's message is clear. It's a message addressed to terorists," Parly said after the raid, according to Reuters. "Those who want to target France, French citizens know that we will find track them, we will find them, and we will neutralize them."
French commandos launched their raid on Thursday night.
The mission was personally approved by French President Emmanuel Macron.
The commandos in the mission were part of Task Force Sabre, a contingent of troops based in Burkina Faso. It was unclear how many troops took part in the raid.
During the onset of the mission, a lookout was killed after he spotted the approaching commandos roughly 30 feet away. The French commandos then hit the nearby shelters after heard the sounds of weapons being loaded.
Four of the kidnappers were killed and two reportedly escaped.
Two French commandos, Cedric de Pierrepont, 33, and Alain Bertoncello, 28, were killed.
Petty officers Cedric de Pierrepont and Alain Bertoncello joined the French Navy in 2004 and 2011, respectively.
"France has lost two of its sons, we lose two of our brothers," France Armed Forces chief of staff Gen. François Lecointre said.
Bertoncello wanted to join the French Navy after graduating highschool, Jean-Luc, Bertoncello's father, said to RTL.
"What he loved was the esprit de corps … he was doing what he wanted and he always told us not to worry … he was well prepared," Jean-Luc reportedly said. "They did what they had to do. For him it ended badly, for the others, it was a successful mission."
The French hostages said they regretted traveling to the area, even after officials warned that it could be dangerous.
They also expressed their "sincere condolences" for Cédric de Pierrepont and Alain Bertoncello.
"All our thoughts go out to the families of the soldiers and to the soldiers who lost their lives to free us from this hell," Laurent Lassimouillas said.
France pays tribute to Petty Officers Cédric de Pierrepont and Alain Bertoncello.
A ceremony was held for Cédric de Pierrepont and Alain Bertoncello at the Invalides, in Paris on Tuesday.
French President Emmanuel Macron described the mission as "necessary" and spoke to family members of de Pierrepont and Bertoncello.
"France is a nation that never abandons its children, no matter what, even if they are on the other side of the world," Macron said in a speech. "Those who attack a French citizen should know that our country never gives in, that they will always find our army, its elite units and our allies on their path."
Special forces soldiers carry the flag-drapped coffins of late special forces soldiers Cédric de Pierrepont and Alain Bertoncello.