Abuja - President Muhammadu Buhari on Wednesday pleaded with militants to "give Nigeria a chance", vowing to keep the country intact despite widespread ethnic and religious divisions that threaten unity.Nigeria is facing security threats on multiple fronts: Boko Haram Islamists in the northeast, Biafran separatists in the southeast, oil rebels in the south and nomadic herdsmen in the central states.There have long been tensions between the Muslim majority north and largely Christian south, which were joined as one entity by former colonial ruler Britain in 1914 for political and economic expediency.Buhari said there had been "a lot of improvement" against Boko Haram, whose seven-year insurgency has killed at least 20 000 people and displaced more than 2.6 million others.Work was now ongoing to tackle the new threat to OPEC-member Nigeria's oil production from rebel groups in the southern delta region, he told senior ministers at a meeting to mark the end of Ramadan."We are now concentrating on the militants to know how many of them [there are] in terms of groupings, leadership and plead with them to try to give Nigeria a chance," he said.Most of the attacks on oil installations since February have been claimed by the Niger Delta Avengers, which wants international oil companies out of the region and fairer revenue sharing of profits.Several other groups have emerged with similar aims but the NDA has also said it wants self-determination for the delta, allying itself with Igbo people in the southeast, who want an independent Biafran republic.Buhari, a former army general who led a military government in the 1980s, referred to his time under General Yakubu Gowon, who was in charge during the Nigerian civil war from 1967-70.That conflict was sparked by a previous unilateral declaration of independence by the Igbo of the southeast."I assure them [the militants] that when we were very junior officers, we were told by our leaders, by the head of state which was General Gowon, that to keep Nigeria one is a task that must be done," he added."We never thought of oil," he said, responding to militant claims that the redistribution of oil revenue across the federation was unfair. "What we were after is one Nigeria. Please, pass the message to the militants that one Nigeria is not negotiable. And I pray they better accept it."