* U.N. Security Council expresses concern over Sahel crisis
* About 18.7 million people in Sahel lacked food in 2012
* France pushing for military mission to reclaim region (Adds further detail on U.S. proposal)
By Michelle Nichols
UNITED NATIONS, Dec 10 (Reuters) - Northern Mali, plagued by Islamist extremists and gripped by an aid disaster, is "one of the potentially most explosive corners of the world," the United Nations warned on Monday, as the United States and France differed over how to tackle the crisis.
Almost 350,000 Malians have fled their homes, with about 40 percent of those sheltering in neighboring countries, said the United Nations. This has exacerbated a humanitarian crisis in the Sahel - a belt of drought-stricken land spanning nearly a dozen impoverished countries on the southern rim of the Sahara from the Atlantic Ocean to the Red Sea.
"Protection concerns are growing, with widespread reports of serious human rights violations from sexual violence and child recruitment to stoning and mutilations of criminal suspects," U.N. High Commissioner for Refugees Antonio Guterres told the U.N. Security Council. "Northern Mali ... (is) one of the potentially most explosive corners of the world."
Mali descended into chaos in March when soldiers toppled the president, leaving a power vacuum that enabled Tuareg rebels to seize two-thirds of the country. But Islamist extremists, some allied with al Qaeda, have hijacked the revolt.
U.N. Secretary-General Ban Ki-moon cautiously recommended last month that the Security Council approve an African Union military operation to take back northern Mali, contingent on political, human rights, training and operational benchmarks being met.
France has circulated a draft resolution to approve such a mission, but the United States has countered with a proposal that the operation be split into two missions that would be mandated separately by the 15-member council, diplomats said.
The United States would like the Security Council to first approve a mission focused on training the Malian army and pursuing a political process before then mandating an international military intervention to retake the north of Mali from the extremists, diplomats said.
France, which has seven nationals held hostage in the desert region, opposes the idea of mandating two missions and wants the council to adopt a single resolution this month, diplomats said.
One senior Security Council diplomat, who spoke on the condition of anonymity, said that the United States was "highly skeptical about the way the French want to go" and have strong doubts about whether a military mission could be successful.
"The U.S. was completely unsatisfied with the state of planning by (West African regional body) ECOWAS for the mission; there's little trust in the African troop contributors that they can do the job, and little trust in the Malian army," he said.
"We are at the beginning of a very long and maybe winding and difficult road toward a resolution," the diplomat said.
Diplomats said the United States believes ECOWAS cannot provide appropriately-trained troops to take on the battle-hardened militants in a desert combat zone.
ECOWAS has agreed to commit the 3,300 troops for an international force in Mali. The troops would mostly come from Nigeria, Niger and Burkina Faso, but other African countries like Chad may contribute troops as well. The European Union is expected to help with the training.
But Ban did not offer U.N. financial support for an initial combat mission in Mali. The African Union has said it would need "a U.N. support package funded through assessed contributions to ensure sustained and predictable support to the mission."
U.S. ambassador to the United Nations, Susan Rice, told the council that the world body must be careful to address the crisis in Mali without destabilizing the entire Sahel region.
Ban's special envoy for the Sahel, former Italian Prime Minister Romani Prodi, told the council that while preparations must be made for a military operation in northern Mali, every effort must be taken to stop the violence and achieve democracy and aid access through peaceful means and negotiations.
"Any military effort in Mali must be undertaken after careful analysis and thorough preparation and that these efforts should be part of an agreed political process that tackles the roots of the conflict," Prodi said. "An extended military action brings always ... not only a humanitarian tragedy but enormous financial costs and an extended period of economic crisis."
Prodi and U.N. peacekeeping chief Herve Ladsous have said that any military action in northern Mali was unlikely to happen until September or October next year.
The EU is planning to send 200 troops to Mali to help with training. But like the United States and former colonial power France, which is the keenest of Western nations for military action, the EU has ruled out a combat role for itself.
Ban told the Security Council on Monday that the crisis in Mali could not be dealt with without addressing the problems of the Sahel, where about 18.7 million people have been affected by food insecurity this year.
"Political turmoil, terrorist activity, drug trafficking and arms smuggling are spilling over borders and threatening peace and security (in the Sahel)," he said. "Extreme climatic conditions and fragile economies only add to this toxic brew of vulnerability."
The Security Council issued a statement expressing serious concern over the insecurity and humanitarian crisis in the Sahel and condemning rights abuses including executions, hostage-taking, people trafficking and recruitment of child soldiers. (Editing by Philip Barbara and Cynthia Osterman)