Maiduguri - Greater international cooperation is required to defeat Boko Haram and neutralise the threat from the Islamist militants in Nigeria and beyond, military commanders and politicians said this week.The jihadists, who are allied to the Islamic State group, have destroyed swathes of remote northeast Nigeria since 2009, killing at least 20 000 people and forcing more than 2.6 million from their homes.Counter-insurgency operations since early 2015 have pushed them out of captured towns and villages to the point where the government in Abuja now believes they are a spent force. But with deadly attacks still a regular occurrence, Nigeria's highest-ranking army officer said a "collective effort" was needed to counter its guerilla tactics - and those of similar groups who have wreaked havoc elsewhere around the world. "We understand the challenges across the spectrum of asymmetric warfare," Nigeria's chief of army staff, Lieutenant General Tukur Yusuf Buratai, said on Wednesday at the headquarters of operations against the militants in the northeastern city of Maiduguri. "This... is a global phenomenon. We must work in synergy to make sure that the terrorism that has been affecting not only here and in the sub-region [of West Africa] but indeed globally" is ended, he added. A regional force comprising troops from Nigeria and its neighbours Cameroon, Chad, Niger and Benin, has helped push Boko Haram out of captured territory since early 2015.WeaponsBut Western nations have largely held back from more direct involvement in the conflict, including sales of weapons and equipment because of the Nigerian army's poor human rights record. US, British, French and German soldiers, among others, are currently present in a "non-lethal" advisory and support roles, in areas from providing Nigerian troops with intelligence and infantry training to tackling the threat from improvised explosive devices. Senior commanders on the ground say the goal now is to develop the Nigerian Army's skills so people can return to their homes and begin rebuilding their lives.President Muhammadu Buhari and his predecessor, Goodluck Jonathan, have said the refusal of Western government the Nigerian military hardware has hampered its efforts to tackle Boko Haram.A $600m deal with the US for 12 fighter aircraft was held up after more than 100 civilians were killed in an airstrike in January this year. Nigeria said this week the purchase had finally been approved. Britain's Foreign Minister, Boris Johnson, also said last month that a request for further equipment was being considered. London's minister in charge of armed forces, Mark Lancaster, who reviewed British Army support programmes across northern Nigeria this week, said "the real key" to improvement was proper basic training, including in human rights. The presence of foreign nations was "a genuine recognition that the problems we face here in Nigeria are not just Nigeria's problems in the northeast", he told AFP. "Not only are they cross-border within the region but of course this is an international problem with an international solution."