France said Thursday it will deploy 3,000 soldiers to combat Islamist violence in the vast and largely lawless Sahel region of Africa.

"Our role is to pursue counter-terrorism in north Mali, the north of Niger and in Chad," Defence Minister Jean-Yves Le Drian said in a television interview.

"We are reorganising our contingent so that 3,000 French soldiers are in that zone."

Le Drian said France was "in the process of ending its frontal war phase" in Mali but added that 1,000 French soldiers will remain, based near the town of Gao in the insurgency-hit northeast of the country.

France launched a military operation in January 2013 to support the Malian army and drive back Islamists advancing on the south. They evicted the rebels from northern Mali towns seized in the wake of a coup in Bamako in 2012.

The French deployment peaked at 5,000 troops, but Paris had pledged to reduce its presence to 1,000 troops by early 2014.

"A certain number of jihadist groups still want to regroup in the North," said Le Drian.

"There are far fewer of them but they have nothing to lose, they have abandoned their lives, so we must fight with extreme precision against any attempt to regroup."

But he said the conflict had entered "a different phase" with UN forces now present in the country and the Malian army rebuilding itself.

Underlining the continued threat in the region, a French soldier was killed by a roadside bomb overnight, the French presidency said.

The death brings the number of French soldiers killed in Mali to eight.

President Francois Hollande expressed his "profound sadness" at the death and added that he had "total confidence in the French forces engaged on the side of Malians and the United Nations forces to continue the fight against armed terrorist groups."

Le Drian said northern Mali remains a "zone of danger, of trafficking of all types".

"We will stay there as long as it takes. There is no time limit."

Earlier this week, Malian military sources told AFP that the rebels in northern Mali have set up a commando unit that has executed alleged collaborators accused of helping French troops and Tuareg rebels.

"At least 11 people accused of being informers for (French military operation) Serval or the (Tuareg) MNLA (National Movement for the Liberation of Azawad) have been slain in the past 11 months by the Islamists," the source said.

Three main groups -- Al-Qaeda in the Islamic Maghreb (AQIM), Movement for Oneness and Jihad in West Africa (MUJAO) and Ansar Dine (Defenders of Islam) -- occupied much of northern Mali for nine months in 2012 and carried out brutal acts against civilians in the name of Islamic sharia law.