GAO — FRENCH troops clashed with Islamist extremists firing rocket launchers outside the north Malian city of Gao, France’s defence minister said on Wednesday.

Jean-Yves le Drian also said there had been "several hundred" jihadist fighters killed and "large" destruction of weapons, giving the first indication of the scope of the combat in an interview on Tuesday on France’s BFM TV.

"It’s a real war … when we go outside of the centre of cities that have been taken, we meet residual jihadists," Mr le Drian said on Wednesday on Europe-1 radio.

Gao has been held by French-led forces since late January, and Tuesday’s clashes highlight complications for the intervention.

Mr le Drian said French aircraft were continuing air strikes every night on suspected militant arms depots and mine-making sites. On the ground, troops have found war materiel, weapons manuals and makeshift laboratories for making improvised explosive devices such as roadside bombs.

"We discovered preparations for a true terrorist sanctuary," Mr le Drian said.

France launched a swift military intervention on January 11 against Islamist extremists who had taken over northern Mali, imposing harsh sharia laws, and started pushing towards the capital, Bamako. A United Nations-authorised African force is starting to take over from French forces in cities seized at the outset of the intervention.

Mali’s minority Tuareg nomads say they are holding several small northern towns, including the strategic city of Kidal, on the road to Algeria. French and Chadian troops entered the city on Tuesday, reports said.

Moussa Ag Assarid of the National Movement for the Liberation of Azawad (NMLA) said its fighters also were holding the northeastern towns of Tessalit, Menaka, Aguelhok and Tinzawatten, as well as Kidal.

Trouble began in Mali, once a stable democracy in West Africa, with the latest in a series of Tuareg rebellions in the north last year. Poorly armed and demoralised Malian soldiers fled before their advance, then staged a coup in the capital, Bamako.

NMLA fighters joined up with Islamist militants linked to al-Qaeda and quickly overran all the main northern cities, including Timbuktu. But the secular fighters fell out with the Islamist extremists when they started imposing sharia laws, including amputating limbs and stoning deaths, and their rebellion was hijacked.

As the extremists have fled the French bombing campaign, it appears the NMLA fighters have returned. They claim to be willing to work with the French forces but not Malian troops they accuse of committing reprisal atrocities against the Tuaregs and Arabs.