IGP, Assam, L R Bishnoi told reporters in Guwahati the operation was launched at Shilajan area of Kokrajhar after receiving specific information regarding movement of the activists of KLO.
After being fired upon by three ultras, the army and the police retaliated and killed the top leader of KLO identified as Dibakar Barman alias Anupal, while two others fled the scene.
A massive combing operation is on to apprehend the two others, Bishnoi said, adding a 7.65-mm pistol along with 7 rounds of ammunition was recovered from the spot.
A defence spokesman said the terrorist had joined the outfit in 2012 following his training in Myanmar.
"His neutralisation is seen as a major success for the security forces as he was capable of perpetrating a lot of trouble in view of the coming legislative assembly elections in the state (Assam)," he said.
Since the last one year police has nabbed 22 KLO militants and killed seven of its top leaders, which he said was a major setback for KLO.
