Eighteen soldiers were killed when "terrorists" struck an army camp in western Niger, the government said Tuesday, adding the US and France had provided air support to help repel the assault.

An armed policeman stands guard on June 19, 2019 at the police checkpoint in Niger. (Photo: AFP)

The attack took place on Monday afternoon at a camp at Inates on the border with Mali, the defence ministry said in a statement. Four soldiers were listed as missing. 

Niger, one of the world's poorest countries, lies in the heart of the fragile Sahel region, which is battling an Islamist insurgency.

"The attack began with the detonation of two suicide vehicles at the entrance to the camp, followed by gunfire from terrorists who arrived on motorbike," the statement said.

"The counter-attack, with air support from our partners (French and American), enabled the enemy to be routed beyond our borders," it said.

"Sweeping-up operations are continuing."

Several "terrorists" were killed, a truck was destroyed by air strikes and two suicide vehicles were destroyed, it said.

On Monday, a military source, speaking on condition of anonymity, told AFP there had been a twin "car-bomb attack" at the camp and suggested the toll would be high.

The base, located in a volatile region, trains Nigerien soldiers to serve in a UN peacekeeping mission in Mali. 

Insurgent groups are active in western and northern Mali, spilling over from a long-running jihadist campaign in Mali, while Nigeria's Boko Haram is present in the country's southeast.