Chairman of Naga rebel group NSCN-K, SS Khaplang, who had engineered many attacks on the security forces, died on Friday at Takka in the Kachin state of Myanmar at the age of 77.
Official sources said that the leader of the Nationalist Socialist Council of Nagaland (Khaplang) who had been ailing for quite some time, died following a cardiac arrest.
Khaplang was a Hemi Naga from Myanmar and was based mostly in that country where the outfit maintains several camps.
Since 1980s, the outfit has engaged in subversive activities, including attacks on security forces, extortion and looting.
Born in April 1940 in Waktham village, east of Myanmar's Pangsau Pass, Khaplang joined the Naga nationalist movement as early as 1964 and was one of the key people in the formation of the NSCN.
However, Khaplang split and formed his own group NSCN(K) in 1988.
He formed the group following differences with the NSCN (IM) leaders Isak Chishi Swu and Thuingaleng Muivah. Swu died in June 2016 in a Delhi hospital.
Khaplang also entered into a ceasefire with the central government in 1997 but abrogated it on March 28, 2015.
Meanwhile, Naga Peoples' Movement for Human Rights (NPMHR) Secretary General Neingulo Krome said the news of Khaplang's sudden demise has come as a "rude shock".
This was so especially at a time when the Naga people are extremely in need of elderly and experienced wisdom of their national movement leaders, to set right the course of the Naga destiny, which is being misinterpreted and re-interpreted in the present day scenario of internal conflicts, he said.
"We will always treasure and cherish his commitment to do what the upcoming Naga generation wants as the Naga national movement is for the well being of future Naga generation who should live in dignity and peace," he said in his condolence message.
There was no immediate reaction from the rebel group or key tribal bodies including Naga Hoho and Naga Mothers' Association.