Two French soldiers were killed in a night-time rescue of four foreign hostages including two French citizens from the clutches of a militant group described as "terrorists" by the military.

President Emmanuel Macron's office said a US woman and a South Korean woman were also freed in the covert operation. All four hostages were safe, the French presidency added. The two French citizens were kidnapped while on safari in neighbouring Benin.

"The precise and determined actions of French soldiers allowed us to take out the kidnappers while protecting the lives of the hostages," France's army chief said in a separate statement.

French special forces carried out the raid under cover of dark over the night of Thursday-Friday, supported by US intelligence and troops from France's Barkhane operation deployed in the Sahel region to counter Islamist militants.

The two French tourists were kidnapped in Benin's Pendjari National Park last week. Their safari guide was found dead, his body riddled with bullets, and their vehicle burned.

The French government had warned its citizens against travelling to parts of Benin near the Burkina Faso border where the park is located because of the risk of kidnapping.

Swathes of northern and eastern Burkina Faso have been overrun by Islamist militants, forcing more than 100,000 residents to flee.