About 11,000 peacekeepers may be needed in Mali to help curb threats posed by militant Islamists, UN chief Ban Ki-moon has said.The peacekeepers may have to be backed up by a second force that will focus on combat operations, he said.France sent troops to Mali in January to wrest control of the north from militant Islamists.It aims to start withdrawing its 4,000-strong force next month and hand over to an African force.French troops, backed by Malian and Chadian forces, have been attacking the militants in desert and mountain hide-outs after they fled the major northern cities, including Timbuktu and Gao.'Counter-terrorism' The Islamists have responded to the French-led campaign by launching guerrilla-style attacks. A suicide bomber killed a Malian soldier at a checkpoint in Timbuktu last week.Nigeria has also sent troops to Mali, but they have not been involved in combat in the north. 'Robust'In a report to the 15-member UN Security Council on Tuesday, Mr Ban proposed that African troops in Mali should operate under a UN mandate.The force should be made up of some 11,200 troops, he said.It would "operate under robust rules of engagement, with a mandate to use all necessary means to address threats to the implementation of its mandate, which would include protection of civilians," Mr Ban said, Reuters news agency reports.He said there may also be a need for a second "parallel force" that would "conduct major combat and counter-terrorism operations and provide specialist support beyond the scope of the United Nations mandate and capability".Diplomats have said France is likely to provide troops for the smaller parallel force, which could be based in Mali or elsewhere in the West Africa region, Reuters reports.Mr Ban also said that with Mali's government weak and no sign of reconciliation between northerners and southerners "elections could provoke further instability or even violence".The army seized power in a coup in Mali last year, but it has since put in place an interim civilian government that has promised to hold elections in July.Islamist insurgents and Tuareg separatists took advantage of the coup to seize control of the whole of northern Mali.The alliance between the Islamists and Tuareg separatists later collapsed, with the Islamists becoming the dominant force in the north.France deployed troops in January, saying the militants could turn Mali in a "terrorist state".