New Delhi, Sep 27 :The Indian Army on Wednesday said it has inflicted "heavy casualties" on NSCN (K) militants during a firefight along the border with Myanmar, but clarified that it was "not a surgical strike". Officials said the incident occurred when a column of the Indian Army was fired upon by "unidentified insurgents". The Army also said the international border was not crossed. "In the early morning hours of September 27, a column of the Indian Army, while operating along the Indo-Myanmar border was fired upon by unidentified insurgents. Our troops reacted swiftly and brought down heavy retaliatory fire on the insurgents," Eastern Command of Indian Army said in a statement. "The insurgents broke contact and fled from the spot. As per inputs, a large number of casualties were suffered by the insurgents. Own troops suffered no casualties during the firefight," it said. The "firefight" took place around 4.45 a.m. on Wednesday morning. The Eastern Command had earlier said in a tweet that the operation was against the Nationalist Socialist Council of Nagaland (Khaplang) militants. "Heavy casualties reportedly inflicted on NSCN(K) cadre. No casualties suffered by Indian Security Force," the Eastern Command said in a tweet. In June 2015, the Indian Army had carried out a surgical strike along the India-Myanmar border on camps of Nationalist Socialist Council of Nagaland (Khaplang) militants, days after an ambush in which terrorists killed 18 Army men in Manipur.