The photo has been used for illustrative purposes.

The attackers struck in a giraffe reserve in the West African country's Kouré area, the governor of Tillaberi, Tidjani Ibrahim Katiella, told Reuters.

The two Nigerians were working as the tourists' guide and driver, AFP news agency reported.

The French foreign ministry said it was making checks into reports of the attack. There was no immediate comment from the government in Niger.

A source close to the environmental services said the assault took place at around 11:30am six kilometres east of the town of Koure, which is an hour's drive from the capital Niamey.

"Most of the victims were shot... We found a magazine emptied of its cartridges at the scene," the source said.

"We do not know the identity of the attackers but they came on motorcycles through the bush and waited for the arrival of the tourists."

The source added that the tourists' vehicle belonged to the French humanitarian organisation ACTED.

The French government warns people against travelling to large parts of Niger where militant groups including Boko Haram and affiliates of Daesh operate.

The Koure Giraffe Reserve southeast of the capital Niamey is a popular attraction in Niger, a huge country that borders seven countries in an unstable region including Libya, Mali, Chad and Nigeria.

Agencies