French forces on Sunday carried out airstrikes in Mali for a third straight day and extended their bombing campaign to the northern strongholds of Islamist forces they are trying to drive out of the centre of the country.

The strikes, designed to support Malian army efforts to push Al-Qaeda-linked groups back to the north of the vast West African state, were reported to have claimed the life of a prominent Islamist leader and up to 100 rank-and-file fighters.

Witnesses said French fighter jets on Sunday struck a camp used by Islamist militants in Lere, around 150 kilometres (95 miles) north of Konna, a key central town which government troops recaptured with French aerial backing on Friday.

French Defence Minister Jean-Yves Le Drian acknowledged that the unexpected advances made by the Islamists last week had not yet been fully reversed as officials admitted they were proving a tougher adversary than anticipated.

"There were (air strikes) last night, there are now and there will be today and tomorrow," Le Drian said in Paris.

"Our intervention is ongoing and we will continue in order to make them retreat and allow Malian and African forces to go forward and re-establish the territorial integrity of the country," Le Drian said.

Aides to French President Francois Hollande described the militants as better equipped, armed and trained than they had expected.

"What has struck us markedly is how modern their equipment is and their ability to use it," one said in a reference to the rebels' hit on a French helicopter which resulted in the death of its pilot, Lieutenant Damien Boiteux, France's only confirmed fatality.

Senior officers from neighbouring countries were expected in Bamako on Sunday to prepare for the arrival of the first troops of a multinational West African force.

The force has been authorised by the UN Security Council to help the Mali government reclaim control of the north of the country and will be commanded by General Shehu Abdulkadir of Nigeria, which will provide around 600 men.

Burkina Faso, Niger, Senegal and Togo all pledged around 500 troops this weekend while Benin has said it will send 300 soldiers.

It remained unclear when any of these forces would arrive and how quickly they could be deployed to the frontline.

A Malian security source said leading Islamist Abdel Krim had been killed in Konna. Krim, nicknamed 'Kojak', was said to be a key lieutenant of Iyad Ag Ghaly, the leader of Ansar Dine, one of the Islamist groups which have controlled northern Mali since last April.

France has been guarded about revealing the exact number of ground troops it will deploy in Mali but media reports have suggested a figure of around 500.

Colonel Paul Geze, the French mission's commander, said the French contingent would be at full strength by Monday and primarily deployed around Bamako to protect the 6,000-strong expatriate community.

Since taking advantage of a power vacuum created by a military coup in Bamako to seize control of huge swathes of Mali in April 2012, the Islamists have imposed an extreme form of Muslim law in areas they control.

Centuries-old mausoleums they see as heretical have been destroyed and perceived offenders against their moral code have been subjected to floggings, amputations and sometimes executions.

In addition to the French helicopter pilot, the conflict has claimed the lives of 11 Malian soldiers, according to an update released on Saturday evening.

A Malian officer in the central town of Mopti, near the front line, said dozens, possibly as many as a hundred Islamists had been killed in Konna.

Human Rights Watch, citing reports from residents, said at least 10 civilians had died as a result of the fighting in Konna, including three children who drowned while trying to flee across the Niger river.

France's intervention has been backed by the main opposition at home, by Britain, which has offered logistical support in the form of transport planes, and the United States, which is considering offering its surveillance drones to help the operation.

Its closest partner Germany has also defended France's action but has ruled out sending any troops and warned that Mali's problems could only be solved by political mediation.