OUAGADOUGOU - New fighting and a crackdown on women not wearing veils by Islamist militants on Friday marred peace moves by two rival groups in Mali's desert north despite pledges they were ready for peace talks with Bamako.

In Islamist-controlled Timbuktu, a local official said dozens of women were arrested on Thursday by Al-Qaeda in the Islamic Maghreb (AQIM) for not wearing veils.

"The Islamists were going into homes to arrest unveiled women," he said.

The women were being "imprisoned" at a disused bank, a medical source added, as AQIM militants vowed to continue the crackdown in the city which they control with Islamist group Ansar Dine, saying "that nothing can prevent them from doing so".

With the north of the country in the hands of a number of Islamist groups, a Tuareg separatist leader meanwhile said his National Movement for the Liberation of Azawad (MNLA) had launched an "offensive" to retake the key north-central region of Gao controlled by the Al-Qaeda linked Islamist rebels of MUJAO (Movement for Oneness and Jihad in West Africa).

But late Friday security sources said the fighting had ended and that the MNLA suffered a "heavy defeat".

An interim administration has been running Mali since the leaders of a March military coup stepped back from power under international pressure in April.

The coup resulted in Tuareg separatists seizing key towns in the north. They were later ousted by the Islamists, giving rise to fears by the international community that the area could become a sanctuary for international extremist groups.

Both AQIM and the less known but associated MUJAO have imposed a brutal form of sharia Islamic law, stoning unmarried couples, amputating thieves' hands and whipping drinkers and smokers.

"The Tuareg of the MNLA suffered a heavy defeat against the MUJAO Islamists. During the fighting, the MUJAO ambushed the MNLA which lost many men," said a Malian security source, which was then confirmed by a regional security source.

There were at least a dozen deaths for the MNLA and at least one death among the Islamists, the source added.

The Islamists sent the MNLA Tuaregs fleeing and "there were even some MNLA soldiers who sought refuge in neighbouring countries", said the security source who requested anonymity.

MUJAO had seized control of Gao in June following battles that claimed 35 lives, leaving the MNLA with no city base.

A spokesman for MUJAO, Walid Sahraoui, said the fighting left "several dead and wounded among the MNLA soldiers", but declined to give figures.

The "offensive" to take Gao came the same day as a high-ranking MNLA delegation announced along with Islamist rebel group Ansar Dine that they were prepared to go into peace talks with the government in Bamako.

A member of the MNLA delegation, Ibrahim Ag Assaleh, claimed that his group had "killed 13 MUJAO fighters... and wounded 17", while the MNLA suffered "nine wounded, one seriously", he said.

In Ouagadougou, the MNLA and Ansar Dine issued a joint statement saying they were "disposed to engage resolutely in a process of political dialogue under the aegis of ECOWAS (Economic Community of West African States) mediation in order to find a negotiated, fair and lasting solution to the crisis."

The statement followed talks with Blaise Compaore, who is Burkina Faso's president and lead ECOWAS negotiator.

The fresh drive by Mali's neighbour Burkina Faso to find a negotiated solution to the crisis, which has effectively split Mali in two, came as plans by regional bloc ECOWAS to send troops into Mali gathered pace.

Ansar Dine has made some conciliatory gestures to the secular MNLA, notably announcing this week that it would not insist on sharia law across Mali but just in its northeastern fiefdom of Kidal.

It has distanced itself from AQIM and MUJAO.

Ansar Dine has also regained favour with the international community by renouncing its separatist ambitions.

The repositioning makes it increasingly likely that the ECOWAS intervention will focus on dislodging AQIM and MUJAO.

The planned force, approved by the African Union, will comprise some 3,300 mainly West African troops. The plan must go before the UN Security Council by the end of the month.

But questions still hang over the operation, particularly its exact composition and financing. It will also require logistical support from countries such as France and the United States.

The European Union also wants to support the effort. Its foreign ministers will meet Monday in Brussels to discuss sending a training mission made up of 200 to 400 European soldiers to Mali in January, according to French sources.

But the international community has made clear it favours a negotiated solution to the crisis.