France's ground troops in Mali advanced on Wednesday towards the Islamist-held north in a bid to flush out jihadist fighters after days of air strikes, as the first Nigerian contingent of a regional force was expected to deploy.

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French armoured units and Malian government forces were heading towards the town of Diabaly, which Al Qaeda-linked groups seized earlier this week even as French gunships and fighter jets pounded their strongholds further north.

"Several hundred Malian and French soldiers left Niono (south of Diabaly) to take" back the town, said a local government official in Niono, while a security source announced plans to "take back Diabaly with the French."

French Defence Minister Jean-Yves Le Drian simply confirmed that ground troops had begun their ground offensive on the sixth day of the former colonial power's intervention in Mali but was short on specifics.

He admitted however that the 800 troops already deployed in Mali faced a long and tough battle against determined fighters whose number he estimated at up to 1,300.

"It's a little more difficult in the west, where we have the toughest, most fanatical and best-organised groups. It's underway there but it's difficult," he said.

French President Francois Hollande said his forces would crush the jihadist militia.

"What do we plan to do with the terrorists? Destroy them. Capture them, if possible," he said on Tuesday during a visit to the United Arab Emirates.

On Tuesday, French soldiers drove out of the capital Bamako in around 30 armoured vehicles. Another convoy was also seen leaving Bamako in a northerly direction.

A company of 190 African troops is expected to arrive in Mali Wednesday, part of a Nigerian contribution that will eventually total 900.

Nigeria is leading the regional force, to which Benin, Ghana, Niger, Senegal, Burkina Faso and Togo have also pledged numbers.

West African army chiefs in Bamako were expected to resume talks on Wednesday on the roll-out of the UN-mandated, 3,300-strong regional intervention force in the former French colony.

Mali has been effectively split in two since March 2012, when Islamists took advantage of a short-lived coup in Bamako and an offensive launched by Tuareg separatists in the north to seize half of the country.

Western countries had voiced fears that Mali's north -- a desert region larger than France -- could become Al-Qaeda's leading global safe haven and be used to launch attacks on targets in Europe.

France had repeatedly ruled out a direct military intervention until Islamist fighters pushed further south last week and were seen as threatening the capital Bamako.

Le Drian said France -- whose surprise intervention was lauded by its allies but has so far attracted limited Western military commitment -- would eventually boost its presence to 2,500 men.

President Francois Hollande stressed however that French troops would not be in Mali for good but would stay until security had been restored and the "terrorists" eliminated.

Hollande will chair a cabinet meeting on the crisis on Wednesday, while Prime Minister Jean-Marc Ayrault attends a parliamentary debate on the intervention. Political reaction at home has been largely supportive.

'Jihadists in it for the long haul'

Since France launched its air offensive on January 11th, Islamists have fled key northern stronghold towns, including ones where they had imposed their brutal version of Islamic law.

But analysts have warned the withdrawal was likely a tactical move.

"The jihadists are in it for the long-haul. They are comfortable in this situation: the vast desert, a difficult terrain, a precarious security situation," said Tunisian Islamist expert Alaya Allani.

One resident in the northern town of Gao reported that the Islamists had cut telecommunication links late on Tuesday, rendering land lines and mobile phones useless.

"They accuse residents of giving information to the (French) soldiers," he told AFP by satellite phone.

The UN and aid agencies have also expressed fears for civilians caught up in the conflict.

So far 144,500 refugees have fled the unrest to neighbouring Mauritania, Niger, Burkina Faso and Algeria, the UN humanitarian agency said on Tuesday, while another 230,000 were internally displaced.

French diplomats and aid agencies plan to meet in Paris and Bamako this week to address the challenge.

Belgium offered two C-130 transport planes and two helicopters to back up France's offensive, while Britain and Canada have offered troop transporters. Germany is considering logistical or humanitarian support.

Hollande met Tuesday with Mauritanian President Mohamed Ould Abdel Aziz, who raised the possibility of participating in the Mali operation, according to the French president's entourage.

Hollande also intimated that Chad and the United Arab Emirates could take part. However, Qatar and the Organisation of Islamic Cooperation, of which Mali is a member, have urged dialogue instead of military intervention.

At home, France has deployed 700 troops in and around Paris, indicating mounting concern over potential reprisal attacks.

Mali's militant Islamists have warned France has "opened the doors of hell" by unleashing its warplanes and called on fellow extremists to hit back on French soil.