French and Niger forces killed three gunmen in a convoy carrying drugs and heavy weapons in Niger close to the Libyan border.

French and Niger forces killed three gunmen in a convoy carrying drugs and heavy weapons in Niger close to the Libyan border, the French army said on Monday, as its troops step up efforts to stop gunmen crisscrossing the Sahel-Sahara region.

Paris, which has led efforts to push back armed group in the region since intervening in its former colony Mali in 2013, has deployed thousands of troops across West Africa to form a counter-terrorism force and prevent trafficking in the region.

The army said in a statement that on May 14 two pick-up trucks attempted to force their way through a checkpoint set up by about 200 French and Niger troops.

"The occupants of the vehicles attempted to drive through and responded to warning shots by violently opening fire," it said.

"Amid the fighting, three people in the convoy were killed and three others were captured and handed to the Niger army," it added.

It said 1.5 tones of drugs and weapons, including submachine guns, were recovered as well as communications equipment.

France has set up a base at Madama in northern Niger to monitor the Salvador Pass trafficking route that leads from southern Libya to northern Mali.