The French-led Barhane force in the Sahel region "engaged its air intelligence capacities to locate the armed group" responsible for the attacks, before on Thursday carrying out air strikes that killed 40 jihadists, the army's general command said.

The Frenchman was among nine people killed this week in two attacks in the W National Park, a wildlife reserve in Benin's remote north bordering troubled Niger and Burkina Faso.

One patrol trying to flush out poachers and another hit two roadside bombs on Tuesday, killing five park rangers, one park official, one soldier and a French trainer, according to a Beninese government toll.

Two days later, a third patrol hit an explosive, killing another park official.

The toll was the deadliest in recent attacks Benin has suffered as coastal West African states face spillover from Sahel countries battling jihadists.

France said on Thursday it had opened an investigation as a 50-year-old citizen was among those killed in a "terrorist attack" in the park.

African Parks, the organisation running the reserve, said the Frenchman had been a "chief law enforcement instructor" there.

Benin had long been one of the more stable countries in West Africa, where militants from the Islamic State group and Al-Qaeda threaten Sahel countries.

Criminal smuggling gangs also operate along its frontier.

In January, two Benin soldiers were killed when their vehicle hit an improvised explosive in the northern Atakora region.