A workshop to make suicide bomber vests has been discovered in northern Mali, the French army has said.
About 5,000kg of fertiliser intended to be used as explosive was also uncovered in Bourem, a town on the Niger River between Gao and Timbuktu.
A sample suicide vest and 18 sewing machines were found and it appears local women were employed there, a French army spokesman told the BBC.
French forces have led an operation to oust Islamist militants from the north.
The al-Qaeda-linked groups had taken advantage of a coup in March 2012 to take control of the north of Mali, including major cities such as Gao, Kidal and Timbuktu where they imposed a strict form of Islamic law.
Since January, about 4,000 French troops with the help of Malian and West African soldiers have gained control of the vast desert region's main towns and cities.
Lt Col Cyril Zimmer, French military spokesman in Mali's capital, Bamako, told the BBC the suicide vest workshop was discovered earlier this week.
The fertiliser found on the site in a remote area of Bourem would be enough for plenty of belts and vests, he said.
Initially the soldiers thought they had found a factory to make copies of uniforms worn by Malian soldiers and those in the West African force, but they later found the sample vest.
The BBC's Alex Duval Smith in Bamako says the discovery comes as France announced it was slowing the withdrawal of its soldiers from Mali.
It will still have between 3,000 and 3,500 troops on the ground when nationwide elections are held at the end of July.
France plans to gradually hand over to the Malian army and a 12,600-strong UN peacekeeping force, which is due to deploy next month and will incorporate the 6,000 West African soldiers already in the country.
The former colonial power intends to keep 1,000 troops in the country to work alongside the UN force to tackle further militant threats.
Earlier on Friday, the French army spokesman in Paris, Col Thierry Burkhard, said that "one third of terrorist groups had been neutralised, one third had decided to give up the game and one third has probably evaporated" to Mali's neighbours.
France decided to intervene in Mali as the militants approached Bamako.