France would back an African military intervention in Islamist-held northern Mali, Defence Minister Jean-Yves Le Drian said on Saturday.

But even if he believed such an operation was inevitable -- and desirable -- it was not for France to take the lead, he added.

"It is not for France to take the military initiative in Mali," he told journalists during a visit to Lorient in northwest France.

He said France "wants it to be the African forces, in particular those of ECOWAS (the Economic Community of West African States) and possibly the African Union, that take the initiative," he said.

An African military intervention in northern Mali was "desirable and inevitable," he added.

"France will support it and, I hope, the European Union also."

At stake was political stability in the south of Mali which was not yet guaranteed, even if interim president Dioncounda Traore had returned to the country from Paris earlier this week, he added.

The situation in the north of the country was "very worrying", said Le Drian.

The hardline Islamists who occupied the vast north in the chaos following a coup in Bamako have tightened control over the area, imposing a harsh form of Islamic law.

Among those now in power in the north are the Islamist group Ansar Dine (Defenders of Faith) and Al-Qaeda in the Islamic Maghreb (AQIM).

Late last month, members of the new Islamist regime dragged an unmarried couple to the centre of the town of Aguelhok for a public stoning, the first reported execution according to strict Sharia law since the takeover.

"We must ... avoid (letting) Mali become a 'Sahelistan'...," Le Drian said, drawing a parallel with hardline Islamist forces in Afghanistan.

He added that he would be discussing Mali with his Spanish counterpart Pedro Morenes later this month, taking time out from a holiday in Spain.

Islamists freed two Spanish aid workers together with an Italian colleague in northern Mali last month: they had abducted them from a Sahrawi refugee camp in Tindouf in western Algeria last October.

Their captors, the previously unknown Movement for Unity and Jihad in West Africa (MUJAO), says it is an offshoot of AQIM.

In a speech on July 14, Bastille Day in France, French President Francois Hollande also said that it was for Africans to decide when and how to intervene in northern Mali, though at the same time he promised unspecified support.

ECOWAS wants to send a 3,000-strong military force to Mali, but is waiting for United Nations approval and a formal request from Bamako.

On Wednesday, ECOWAS pledged support for Mali's interim president Dioncounda Traore, after mediators extended a deadline for the country to form a unity government.

Diarra's interim government was set up in April to take over from the junta which seized power on March 22.

It was in the wake of the March military coup in the south of the country that hardline Islamists and Tuareg rebel forces seeking an independent homeland seized control of the north.

The Islamists subsequently forced out the Tuareg nationalists to take control of the region and imposed Sharia law.

The five-month-old conflict has forced 260,000 Malians to flee to neighbouring countries, UN High Commissioner for Refugees Antonio Guterres told reporters Friday after a visit to the region.