French warplanes hit a town newly-seized by Islamists in Mali as African troops on Tuesday prepared to join the offensive which has sent the jihadists fleeing from their northern strongholds.

France on Monday secured UN backing for its campaign launched four days earlier to halt a southward advance on the capital Bamako by Islamist fighters who have controlled northern Mali since April.

A contingent of 750 French troops has been sent to bolster Malian forces against the well-armed rebels. Defence sources say the force will eventually rise to 2,500.

Since the French air offensive was launched on Friday, the Islamists have fled three key towns under their control: Timbuktu, where residents have suffered some of worst abuses of the past 10 months, as well as Gao, also in the north, and Douentza in Mali's centre.

Though driven from their strongholds by French Rafale fighter jets, the Islamists struck back Monday in the government-held south, capturing the small town of Diabaly some 400 kilometres (250 miles) north of Bamako.

French planes hit Diabaly overnight, according to a security source who told AFP at least five Islamists were killed and many injured. A resident of a town some 20 kilometres (12 miles) from Diabaly told AFP he had seen armed Islamists fleeing after the strikes.

President Francois Hollande, speaking from the French military base in Abu Dhabi, said the night's strikes had "achieved their goal".

France and other UN Security Council countries want to speed up the deployment of a UN-mandated 3,300-strong west African intervention force in Mali, held up by disagreements among its contributors.

West African army chiefs will meet in Bamako later Tuesday to plan the deployment.

Nigeria, which will lead the force, plans to have 600 troops on the ground in Mali "before next week," President Goodluck Jonathan said. Benin, Ghana, Niger, Senegal, Burkina Faso and Togo have also pledged troops.

But experts have warned it could take months before the African troops are fully operational.

The 15-nation UN Security Council on Monday expressed its unanimous "understanding and support" for the offensive, France's UN ambassador Gerard Araud said.

But the Organisation of Islamic Cooperation, of which Mali is a member, called Tuesday for an "immediate ceasefire, dubbing the offensive "premature" and urging all parties to return to the negotiating table.

So far the unrest has caused nearly 150,000 people to flee the country, while another 230,000 are internally displaced, the UN humanitarian agency said Tuesday.

The UN High Commissioner for Refugees has registered 144,500 refugees in neighbouring countries -- 54,100 in Mauritania, 50,000 in Niger, 38,800 in Burkina Faso and 1,500 in Algeria, OCHA said.

The hold by Al-Qaeda linked armed Islamists on vast swathes of Mali's northern desert had sparked fear in the international community that the zone could become a breeding ground for terrorists.

While France has made quick gains in eastern Mali, French Defence Minister Jean-Yves Le Drian has said the situation is more difficult in the west where the rebels are better armed.

Scores of French armoured tanks from a base in Abidjan arrived in Bamako overnight along with extra troops, a spokesmen for the French forces told AFP.

Belgium has said it will contribute two C-130 transport planes and a medivac helicopter to back up the French offensive, while Britain and Canada have offered troop transporters and the United States has pledged to share intelligence and provide logistical support.

A spokesman for the Ansar Dine (Defenders of the Faith) rebel group, Senda Ould Boumama, said their withdrawal from northern cities was a "tactical retreat" to reduce civilian casualties, in comments published on Mauritanian news website Alakhbar.

Meanwhile a leader of the Movement for Oneness and Jihad in West Africa (MUJAO) vowed revenge. "France has attacked Islam. We will strike at the heart of France," warned Abou Dardar of the Al-Qaeda-linked group on Monday.

And Afghanistan's Taliban insurgents condemned France's military intervention, warning that it would have "disastrous" consequences.

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