BAMAKO (AFP) - Caught off guard by France’s fierce offensive against their bases, Islamists occupying northern Mali have fled into the vast desert to regroup and plot their next move, experts said Tuesday.

Masters of the harsh desert terrain, experts of survival and well-armed, the jihadists’ retreat should not be mistaken for a sign of defeat, analysts said.

Terrorism expert Jean-Charles Brisard said the Islamists’ evacuation of their bases after heavy air strikes by French fighter jets was an obvious “tactical retreat.”

He said the insurgents were merely taking advantage of “the immensity of the desert” of northern Mali, whose main towns they have controlled since overpowering a weakened Malian army in April.

“To our knowledge they have retreated into the mountainous regions around Kidal. It will be necessary to quickly go on the ground to dislodge them,” he said.

The first troops from a regional West African force were bound for Mali on Tuesday to shore up a five-day old French military offensive that has uprooted the insurgents from several key strongholds.

Defence sources said France plans to triple its force from a current 750 to a total of 2,500 troops, sign that Paris is preparing for a drawn-out campaign to stem the advance of jihadists who have held northern Mali since April.

And West African army chiefs met Tuesday in Bamako to plan the roll-out of a UN-mandated, 3,300-strong West African intervention force in the former French colony.

“We are here today to speak about the engagement alongside our Malian brothers in arms, to liberate the north of Mali,” Ivory Coast army chief General Soumaila Bakayoko said at the talks. Nigeria, which is leading the force, said the first of its troops would deploy to Mali within 24 hours.

Defence spokesman Colonel Mohammed Yerima said Nigeria’s total commitment will be 900 troops, 300 more than earlier announced.

Benin, Ghana, Niger, Senegal, Burkina Faso and Togo have also pledged troops.

Since France launched its offensive, the Islamists have fled key strongholds under their control as Rafale fighter jets blasted the areas of Gao and Kidal in the north, and Douentza in Mali’s centre.

Residents also reported the Islamists had fled Timbuktu, which has not been targeted by the French strikes.

On Tuesday cultural agency UNESCO urged Malian and French forces fighting in Mali to protect ancient cultural sites during air raids and ground attacks. 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.

French President Francois Hollande, speaking from a French military base in Abu Dhabi, said Tuesday the latest strikes had “achieved their goal”. He defended the French intervention, saying it had prevented Mali from being overrun by “terrorists”.

The 15-nation UN Security Council on Monday expressed its unanimous support for the French offensive.

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 negotiations.

So far the unrest has sent 144,500 refugees fleeing to neighbouring Mauritania, Niger, Burkina Faso and Algeria, while another 230,000 are internally displaced, the UN humanitarian agency said Tuesday.

The fighting has also left at least 11 Malian soldiers dead and one French helicopter pilot.

The hold by Al-Qaeda-linked Islamists on vast swathes of Mali’s northern desert has fuelled fears the zone - a hostile, semi-arid region more than double the size of France - could become an Afghan-style breeding ground for terrorists.

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

Belgium has said it will contribute two C-130 transport planes and a medivac helicopter, while Britain and Canada have offered troop transporters.

US Defence Secretary Leon Panetta reaffirmed Tuesday that Washington - which has pledged intelligence and logistical support - stands ready to support France’s military assault, but without putting any US troops on the ground. And EU diplomats said European Union foreign ministers would meet Thursday to speed up the dispatch of a mission to train Mali’s army and discuss how best to back up the African force.

Hollande met Tuesday with Mauritanian President Mohamed Ould Abdel Aziz, who raised the possibility of participating in operation “Serval” if asked, according to Hollande’s entourage.

The French president also intimated that Chad and the UAE could take part.

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

Leaders of the militant groups under attack have warned France has “opened the doors of hell” by unleashing its warplanes and have called on fellow extremists to hit back on French soil.

Afghanistan’s Taliban have joined in condemning France’s intervention, warning of “disastrous” consequences.

The Taliban said in a statement on their website that France should have learned lessons from the “failed” wars in Afghanistan and Iraq.

“When France began its withdrawal process from Afghanistan in recent times it seemed as the French government would likely expand its anti-war stance to other regions of the world,” spokesman Zabihullah Mujahid said.

“France has launched war against the Muslim nation of Mali without having any legal jurisdiction,” the Taliban said, urging governments and global organisations to “stop such transgressions”.