France has delayed plans to pull troops out of its former colony Mali after a fresh bout of clashes in a key town.

France said earlier this month it was ending its "frontal war phase" in Mali after sending troops there in 2013 to free the country's vast desert north from Islamists and Tuareg rebels who seized control after a coup.

It planned to redeploy 2,000 of its 3,000 remaining troops serving in Mali under an operation named Serval to other countries in the Sahel region.

But a French defence source said the redeployment had been delayed after fighting between rebels and the army in the flashpoint northern town of Kidal.

"Given the events of the last 48 hours, the operation to restructure the forces under Serval and send them to other French units in the Sahel-Sahara region has been deferred by a few weeks," the source said.

Defence Minister Jean-Yves Le Drian had been due to go to Mali and Chad at the weekend for a reorganisation of the deployment, but has cancelled the visit, the source said.

Tuareg separatist rebels clashed with Malian soldiers in the northern town of Kidal during a visit by Prime Minister Moussa Mara, whose government is backed by French soldiers who have helped dislodge rebels and armed Islamic extremists from northern towns.

The fighters of the National Movement for the Liberation of Azawad (MNLA) took 32 civil servants hostage but released them on Monday. The battle left eight Malian soldiers and 28 rebels dead.

Malian President Ibrahim Boubacar Keita welcomed the released hostages as they stepped off the plane that brought them back to Bamako.

"You have been to hell and back," he said.

Sources in the UN force assisting French and Malian forces in peacekeeping efforts in the restive north said several hundred people had fled their homes to Kidal to the relative safety of nearby desert camps.

A French-led initiative last weekend saw pledges by west African countries and France and the United States to fight Nigeria's Boko Haram Islamist group together, with joint surveillance and intelligence sharing.