abuja nigeria president muhammadu buhari say country afford go back dark days insecurity oil-producing niger delta region speech present 2018 budget buhari call side maintain dialogue last week militant group niger delta avengers threaten brutal bloody return violence last year slash oil output oil minister emmanuel ibe kachikwu visit region week attempt maintain ceasefire buhari also say country exemption production cut organize organization petroleum export countries significant help country challenge time nigerian president say afford return delta insecurity