* French air raids hit rebel targets around Timbuktu
* Clinton sees "serious, ongoing" Qaeda threat in Mali
* Nigerian, S. African leaders fear spread of insurgency
* Still questions over capacity, funding of African force
DIABALY/SEGOU, Mali, Jan 23 (Reuters) - The United States and African leaders threw their full diplomatic weight on Wednesday behind a campaign to expel Islamist rebels from Mali, as French air strikes harried the al Qaeda-allied fighters in their strongholds.
For nearly two weeks, French jets and helicopters have been hitting carefully selected targets around rebel-held Malian towns such as Gao and Timbuktu, while African troops gather for a planned ground offensive against the Islamist forces.
Last week's bloody seizure of a gas plant in neighbouring Algeria by Islamist guerrillas opposing the French action in Mali - in which at least 37 foreign hostages were killed - heightened fears in Africa and the West that Mali's north could become a launchpad for international attacks by al Qaeda.
After halting a surprise Islamist offensive southwards towards Mali's capital Bamako, French ground troops and Malian army soldiers backed by French armoured vehicles are securing locations recaptured from the rebels in the last few days.
At one of these, Diabaly, a town of mud-brick homes 350 km (220 miles) north of Bamako, jubilant residents welcomed foreign reporters and showed them munitions abandoned by the fleeing Islamist fighters, including several six-foot long shells.
Charred rebel pick-up trucks destroyed by the French air strikes were also visible amid the mango trees.
The U.N.-mandated intervention in Mali was originally conceived as "African-led, African-owned", but with the Malian army in disarray and African neighbours scrambling to deploy troops, France has taken the lead in the operation.
Amid widening international support for the Mali operation, the European Union is preparing a 450-member mission to help train the Malian army while the United States and European governments are helping fly in French troops and equipment.
Voicing U.S. backing, Secretary of State Hillary Clinton described the internationally-backed intervention in Mali as a response to "a very serious, ongoing threat" posed by the regional affiliate of al Qaeda and its local allies.
"We are in for a struggle but it is a necessary struggle. We cannot permit northern Mali to become a safe haven," she said in Washington, referring to Malian elements of al Qaeda as not only a "terrorist syndicate" but also a "criminal enterprise".
African governments, critical in the past of what they saw as meddling by former colonial powers like France, are now embracing the French-led action as a way to avoid a broadening Islamist insurgency in Africa.
"All of the African continent, all its heads of state, are happy about the speed with which France acted and with France's political courage," African Union Chairman Thomas Boni Yayi, who is president of Benin, said during a visit to Germany.
Nigeria, Africa's No. 1 oil producer, is contributing 1,200 troops to the Mali intervention force, even though it is struggling to control a bloody Islamist insurgency at home by the sect Boko Haram. U.S. and African military officials say Boko Haram has links with al Qaeda and its allies in Mali.
"If it is not contained, definitely it will spill into West Africa... It is one of the reasons we have to move fast," Nigerian President Goodluck Jonathan told a panel at the World Economic Forum in Davos, Switzerland.
South African President Jacob Zuma, who leads Sub-Saharan Africa's biggest economy, said the Mali situation would figure high on the agenda of an African Union summit this weekend.
"It is not just Mali. It is Chad, it is Niger, it is Mauritania," Zuma told Reuters in an interview in Davos, adding that South Africa could play a role in Mali if asked to by the African Union as the continent's top representative body.
TIMBUKTU "GADDAFI HOUSE" HIT
Among the rebel targets in Timbuktu hit by French airstrikes in the last few days was a house built there by the late Libyan leader Muammar Gaddafi, which Islamist militants were using as a base, local residents said.
The Islamist alliance in the north, which groups al Qaeda in the Islamic Maghreb and the Malian militant groups Ansar Dine and MUJWA, holds the major towns of Timbuktu, Gao and Kidal.
Mali's state radio reported that, besides the Gaddafi house in Timbuktu, rebel fuel and weapons depots around the fabled Saharan trading town were also bombarded in the French raids.
With these keeping the rebels on the defensive, military experts say the swift and effective deployment of African ground forces is crucial to sustain the momentum of an offensive against the Islamists and prevent them melting away into empty desert or rugged mountains near the Algerian border.
"The recovery of Mali's sovereignty is under way," French Defence Minister Jean-Yves Le Drian told France 24 TV, adding that the African force for Mali, known as AFISMA and expected to number more than 5,000, was being deployed.
Around 1,600 of its members were already in the West African state, a French official said.
These came so far from Benin, Nigeria, Senegal, Togo and Niger. Chad, a Central African state whose troops are experienced in desert warfare, was also moving troops towards Mali's border in neighbouring Niger to assist in the mission.
Ivory Coast said on Wednesday it was sending a 500-strong logistical support contingent to Mali, but no combat troops. Ghana and Guinea were also contributing to the African force, French Prime Minister Jean-Marc Ayrault said.
The European Union's military training mission in Mali (EUTM) would be launched in mid-February and led by a French general, but would have no combat role.
WHO WILL PAY?
International donors are due to meet in the Ethiopian capital Addis Ababa on Jan. 29 to discuss the African military operation in Mali, and France said they would be asked to provide about 340 million euros ($452 million.
France's Le Drian told France 24 that the 12-day-old French military operation in Mali had cost 30 million euros so far.
Despite the widespread declarations of support for the Mali intervention, some analysts questioned whether western powers like the United States were following up on their words with sufficient concrete action and support to ensure its success.
"There is not much money for Africa... It's a low priority" for Barack Obama's U.S. administration, said Vicki Huddleston, who served as U.S. ambassador for Mali in 2002-2005.
"We have to come up with a really serious 'boots on the ground' strategy," she told Reuters, adding that Islamist militants in North and West Africa were "looking for their next target". (Additional reporting by Emma Thomasson and Ben Hirschler in Davos, Stephen Brown in Berlin, Tiemoko Diallo in Bamako, Andrew Quinn in Washington, John Irish and Elizabeth Pineau in Paris, Joe Bavier in Abidjan, David Lewis, Daniel Flynn and Pascal Fletcher in Dakar; Writing by Pascal Fletcher; Editing by Tom Pfeiffer)