Ghana's President John Dramani Mahama has warned that Islamist militancy poses a threat that could destabilize the whole of West Africa.Mr Mahama told the BBC that although Ghana had not been directly affected, no country was safe if insurgency was allowed to take hold elsewhere.He said intervention led by France had helped guarantee stability in Mali, but the conflict there was not yet over.He also backed the African Union's plan to create a rapid reaction force.Mr Mahama said there had been a suggestion that it could be funded by a tax on air travel and hotels across the continent.'Attractive foothold'In January, French forces spearheaded an operation to drive out al-Qaeda and other allied Islamist groups from northern Mali, where they had seized control in the chaos following a coup last year.Ghana's leader said the incident showed how the whole Sahel region had "become an attractive foothold for insurgents"."If we allow that foothold to consolidate, then it could affect the stability of our entire region," Mr Mahama told the BBC's Newsday programme.Despite regaining territory from Islamist groups in Mali, he said the crisis was not over."There is the danger of asymmetric attacks like we saw in Niger the last few days, and so it is a matter that worries all of us in the sub-region," Mr Mahama said."And we need to act collectively as a sub-region and a continent and indeed globally to be able to ensure peace and stability."