France secured fresh UN backing for its military action in Mali and reinforced its ground forces with an armoured column after driving Islamists from their northern bases with air strikes.

A meeting of the 15-nation UN Security Council on Mali expressed unanimous "understanding and support" for the military intervention, France's UN ambassador Gerard Araud told reporters late Monday.

The United Nations also said more than 30,000 people had fled the fighting and accused the Islamists of stopping thousands of them from travelling south into government-held zones.

French President Francois Hollande meanwhile arrived in the United Arab Emirates early Tuesday on a long-planned trade mission, but his aides have insisted he will be kept fully informed of developments in Mali.

Defence Minister Jean-Yves Le Drian, originally scheduled to be part of the high-powered delegation, stayed in Paris.

French jets on Monday hit Douentza, 800 kilometres (500 miles) from Bamako, which the Islamists have held since September. But residents said the fighters had left before the warplanes arrived.

The jihadists have imposed a brutal version of Islamic law in the north for nearly 10 months.

In Timbuktu, where residents have been executed or had limbs cut off in some of the worst abuses, they said the Islamists had fled in anticipation of an attack.

In Gao, another northern city formerly held by the Islamists, they were nowhere to be seen after bombing by Rafale warplanes on Sunday, residents there reported.

Having been driven from their northern strongholds Monday, the Islamists struck back in western Mali, capturing the small town of Diabaly from the country's weakened army. Diabaly lies some 400 kilometres north of Bamako.

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

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," Abou Dardar of the Al-Qaeda-linked group said Monday.

Meanwhile French Prime Minister Jean-Marc Ayrault acknowledged the plight of the eight French hostages being held in Africa and the risks that the Mali operation might pose for them.

However, he said: "To do nothing and let Mali become a haven for terrorist groups would not have contributed to the freeing of our hostages."

On top of the use of Rafale fighters and helicopter attacks, about 650 French troops are in Mali to halt the Islamist advance, according to the French defence ministry.

Around 30 French armoured tanks and troop transport vehicles crossed from Ivory Coast into Mali on Monday, escorted by a helicopter, witnesses said. France has a 450-strong force based in Ivory Coast supporting a UN peacekeeping mission there.

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.

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

Britain and Canada have offered troop transporters to the French military and the United States says it will share intelligence and provide logistical support.

Algeria said it had closed its 2,000-kilometre desert border with northern Mali to stop Islamists crossing into the country. To the west, Mauritania said it had sent soldiers to close its border with Mali.

The Islamists seized upon the chaos of a military coup in Bamako last March to seize northern Mali, sparking widespread international fears that they could set up a terrorist safe haven.

When the UN Security Council approved an African-led intervention force, UN officials said it could not be launched until September.

But the Islamist offensive and France's military intervention led diplomats to predict a review of those plans.