Ecowas wants Tuaregs to help take on militants as officials say priority is to remove all terrorists

West African officials are pushing the Mali government to offer Tuareg separatists in the north of the country autonomy in exchange for joining the fight against hardline al-Qaida-linked terrorists, the Guardian has learned.

The regional bloc of the Economic Community of West African States (Ecowas) also hopes to boost their efforts to flush out militants from northern Mali by persuading moderate members of one of the powerful Islamist groups controlling the region to join forces with Tuaregs.

Granting the Tuaregs any kind of autonomy in exchange for their support would reverse the policies many Tuaregs have fought to overturn since Mali's independence 52 years ago, and could embolden dozens of separatist movements across West Africa.

Malian officials said four government representatives have this week been appointed to lead discussions with the Tuareg independence movement, the Mouvement National de Libération de l'Azawad (MNLA) and moderate members of the Islamist Ansar Dine movement.

"Autonomy … is not off the cards. But there has to be a solid agreement between all parties. The priority is to get rid of all terrorists who have no right to be [in northern Mali]. Once that happens, the Malian state will determine the framework in which conditions of autonomy could be granted," a government official involved in the discussions told The Guardian. The official spoke on condition of anonymity owing to the sensitivity of the matter.

The negotiations, which will be pursued as well as military intervention, are likely to be protracted, and complicated by the fact that only a fraction of Mali's northern ethnic groups are Tuaregs, not all of whom want independence, the official added.

The new strategy is being pursued as military documents obtained by the Guardian show an intervention force by Ecowas to retake the north is unlikely before September, giving Islamists time to strengthen their position. In the meantime, mediators from the bloc appear to be pressing Mali into reconsidering its decades-old position on the Tuaregs. The indigo-turbaned Tuaregs traditionally roam the Sahara, where al-Qaida splinter groups have flourished, and which stretches across 10 African countries.

Djibril Bassolé, the Burkina Faso foreign minister mediating between the Mali government, based in Bamako in the south, and northern-based groups, said: "Mali cannot accept the imposition of sharia [law] through arms. But they can look at a form of autonomy, decentralisation or power-sharing if Ansar Dine and the MNLA lay down their weapons. Both groups have reiterated their willingness to cooperate with the government on that basis."

In April, angry Malian officials called a Tuareg declaration of independence "null and void", but the mood has changed as the government has been pushed by Islamist extremists. Their armed campaign to impose sharia law on the moderate Muslim nation has left a trail of rights abuses the army has been powerless to stop.

"The idea is that after the liberation of the north, Mali will give Azawad some autonomy. The most likely model is [neighbouring] Niger, where the Tuaregs of Agadez and Zindar are semi-autonomous," said a senior Ecowas negotiator who confirmed the plan had been tabled.

Similar separatist groups in the region, such as Morocco's Polisario Front and Senegal's Casamance militants, who have fought hard to redraw Africa's colonial borders, will be following the developments closely.

Galvanised by arms from Libya's conflict, the MNLA toppled Mali's army in June, splitting the country in two as they sought to carve out an independent nation called Azawad. But criminal gangs and al-Qaida affiliates who poured in alongside them have since routed the Tuaregs. An area the size of France and Spain combined is now under the control of Ansar Dine, al-Qaida in the Islamic Maghreb (AQIM), and the Movement for Tawhid and Jihad in West Africa (Mujao).

Ansar Dine have carried out amputations, banned telephone ringtones and razed shrines in their attempt to impose sharia law across Mali, but that alienated some members of the movement. Moderates, regional leaders believe, could be persuaded to form a military and political alliance with the MNLA. Officials declined to comment on whether any military coalition involving the Tuaregs would be armed or fight alongside government forces.

Headed by relatives from the same clan, Ansar Dine and the MNLA initially fought alongside each other, though the former had resolutely Islamist goals, while the latter was mainly interested in carving out its own territory. But the relationship between its leaders has since turned "sulphurous," an MNLA official said. Spokesperson Moussa Ag Acharatoumane said the group was willing to "put differences on hold" and unite in a military alliance against al-Qaida affiliates.

Moderates could weaken Islamist groups by splintering them but a blaze of renewed fighting this week highlighted the risks of backing any rebel group. In the worst case scenario, officials admit, a messy clannish scramble for power could ensue.

"It's a very, very delicate question who to let on side. It's a marriage of convenience but there are groups with vested interests who may work with the government now, turn against them tomorrow," an African diplomat also involved in the talks said.

The delay in a planned international offensive came as French president François Hollande confirmed a French national had been kidnapped on Tuesday in the south-west Mali town of Kayes, near the border with Senegal and Mauritania. France has been using drones for surveillance in Mali but will not send ground troops.

Ecowas, backed by the African Union, will present the United Nations security council with a battle plan to retake the north at the end of this month that calls for 180 days to train and equip 3,300 Ecowas troops and Mali's army, operations papers obtained by the Guardian showed. The delay is likely to stretch into September owing to seasonal rains.

"The majority view is that military intervention is unlikely to take place before September. Before then, the more people who can be removed from the battlefield through negotiations, the better," said a Bamako-based diplomat.

A small but well armed network of extremists has continued to dig in across Mali's lawless desert. "The strength of the core fighters from various nationalities of all movements is estimated to be between 2,500 and 3,000 coming from Africa, Europe and Asia," the battle document said. A list of weapons available to them included anti-aircraft guns and surface-to-air missiles.

Attempts to flesh out combat plans have also snagged on the reluctance of some countries to pitch their troops into a conflict with no obvious exit strategy, insiders added. Algeria, a key regional power, "had not warmed to the idea of intervention," the Ecowas negotiator said.

Although they are not members of Ecowas, Algeria and Mauritania – who share thousands of kilometres of borders across the Sahara – are expected to play a role, according to officials. The two countries have substantial and vital desert training, military officials say.

About 400,000 people have been displaced by the conflict.