The fall of Mali's north to Islamist groups, including al Qaeda's North African wing AQIM, has created a haven for militants and international organized crime groups in West Africa, stirring fears of attacks in Europe.

"We intend to move forward fairly quickly," Foreign Ministry spokesman Philippe Lalliot told reporters. "It's a resolution that could be voted between December 10-20."

France is the most vocal Western backer of a plan for African troops to retake northern Mali. Seven French nationals are being held hostage in the desert region.

UN Secretary-General Ban Ki-moon said on Wednesday a war plan drafted by African leaders was incomplete, leaving open questions about how the force would be commanded, trained and equipped.

Ban did not offer UN funding for the mission and voiced reservations about the United Nations' capacity to take on "terrorists and affiliated groups".

Lalliot played down Ban's reservations about the strategic operations plan, saying it was normal that details still needed to be finalised.

The current head of the African Union, Benin President Thomas Boni Yayi, sent a letter on Thursday expressing frustration over the slow progress in mobilising an international force to retake northern Mali.

"Any reticence about a military intervention would be interpreted as a weakness and give fighters allied to al Qaeda time to take more territory," the letter said, according to an excerpt provided by Benin's presidency.

Ansar Dine, an Islamist group linked to al Qaeda, moved into a town near Mali's border with Mauritania on Thursday after separatist Tuareg rebels withdrew without a fight.