Mali's regional neighbours are wary of sending a military mission to the chaotic nation without a clear mandate, after Islamist extremists and Tuareg rebels seized the country's vast north, security sources say.

The 15-nation Economic Community of West African States (ECOWAS) has raised the prospect of sending a force of up to 3,000 men to try to reclaim the north, seized in a lightning push by rebels, outlaws and Al-Qaeda-linked fighters who capitalised on the disarray of a March 22 coup in the capital Bamako.

Meeting last week in Ivory Coast, ECOWAS army chiefs said they had hammered out terms of possible military intervention, still to be put to heads of state.

Neighbours are nervous about an Islamist-controlled northern Mali becoming a rogue state that would cultivate extremist thinking and prompt an outpouring of refugees into the food-scarce region.

But some countries are jittery about committing troops without a clearly defined mission, while others question whether ECOWAS has the technical and logistical capabilities to mount a desert campaign.

"ECOWAS has the men, what is needed is to define the mandate," a senior military official from Burkina Faso involved in mediating the crisis told AFP.

"Is stabilisation or the recapture of the north the objective?" a Western security official in the region said.

Despite ECOWAS' assertions, some security sources suggested that raising and supporting the needed forces could be problematic.

Regional powerhouse Nigeria, which has previously provided peacekeepers to multi-lateral forces, could be reluctant this time, as it is struggling to contain the Boko Haram Islamist insurgency within its own borders.

Speaking in Abuja, Nigerian foreign ministry spokesman Ogbole Amedu Ode said only that Nigeria would "work in tandem with ECOWAS" on the Mali crisis.

A member of the Malian parliament said Monday that among the rebels controlling Gao were dozens of Boko Haram militants, information confirmed by later reports.

Liberia has bluntly stated it will not send troops, and politically unsettled countries like Guinea and Guinea-Bissau are also expected to resist military involvement.

According to a security official, several hundred men from the West African contingent in the UN's mission in Ivory Coast could be redeployed.

"But that would be a motley group of questionable quality," said the official, who requested anonymity.

Outside support would also be needed. "We don't have the logistics, the vehicles and planes to send the troops," the military official from Burkina Faso said.

France, Mali's former colonial power, would however be ready to provide logistical support for ECOWAS, French Foreign Minister Alain Juppe has told AFP.

Juppe estimated the number of well-trained armed fighters in northern Mali at about 1,000.

Despite the potential pitfalls, a multi-lateral intervention could provide a chance to weaken Al-Qaeda in the Islamic Maghreb, a group that has kidnapped Westerners in the Sahel, a region on the southern edge of the Sahara desert.

The jihadists are backing Mali's Islamist Ansar Dine group, led by charismatic former Tuareg leader Iyad Ag Ghaly, who has reportedly imposed Islamic sharia law in areas under his control.

The main Tuareg rebel group, which declared independence for the northern territory it conquered, said Friday it was ready to help fight the "terrorism" of Al-Qaeda's north African branch.

"The National Movement for the Liberation of Azawad has clearly stated its demarcation from Al-Qaeda in the Islamic Maghreb and its willingness to act within the framework of a mobilisation of all countries concerned by this curse," its representative in Paris, Mossa Ag Attaher, told AFP.

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