The NIA on Monday said it has arrested a self-styled regional commander of Naga militant outfit NSCN-K who masterminded the June 4 ambush on an Indian Army convoy in Manipur.According to the National Investigation Agency (NIA), Khumlo Abi Anal, regional commander of the National Socialist Council of Nagaland-Khaplang (NSCN-K), was arrested from Chandel district of Manipur.Eighteen army personnel were killed and 15 seriously wounded on June 4 when a convoy of 6 Dogra Regiment was ambushed by NSCN-K militants in Paraolong village in Chandel district bordering Myanmar.