Officials said the hostages and their captors were in transit in Burkina Faso and the kidnappers meant to take them to Mali.
The US military supported the French-led operation to free the four hostages, according to two US officials.
She and a Korean woman were rescued, along with two Frenchmen who were kidnapped while on a safari in neighboring Benin about two weeks ago. "We were not aware of their presence. the American will be repatriated separately", Parly said. The military operation was initially launched to rescue two French tourists snatched earlier this month, before they could be handed over to militants in Mali.
Lassimouillas, his compatriot, Patrick Picque, and the South Korean landed safely Saturday at a French air force base outside Paris, where French President Emmanuel Macron greeted them. They expressed regret over what happened and French officials say their captors were "terrorists" who planned to transport them to an Al Qaeda affiliate in Mali.
Four kidnappers were killed in the raid, the French army said, adding that the USA military had provided intelligence.
It warns of "the presence of armed terrorist groups and the risk of kidnapping".
The badly disfigured body of their wildlife guide was found shortly afterwards, as well as their abandoned four-wheel Toyota truck.More news: Eden Hazard drops major hint regarding his Chelsea future
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The other two liberated hostages had apparently already been in the kidnappers' hands for 28 days, General Lecointre said.
Laurent Lassimouillas is one of the four ex-hostages freed.
"We are grateful for the safe recovery of hostages, including an American, during a recovery operation in Burkina Faso", said Tibor Nagy, the U.S. assistant secretary of state for Africa, on Friday. Swathes of northern and eastern Burkina Faso have been overrun by Islamist militants, forcing more than 100,000 residents to flee.
Parly also thanked local authorities and the "precious support of our American allies in conducting this operation".
He and Mr Picque are to return to Paris later Saturday, where President Macron and Mr Le Drian are to meet them at the Villacoublay military airport southwest of the capital.
A total of 24 French soldiers from the Barkhane force have died in the region since 2013 when France intervened in Mali to drive back jihadist groups who had taken control of the north of the country.
Burkinabe security and intelligence forces assisted in the operation.