Isak Chisi Swu, chairman of the National Socialist Council of Nagaland (NSCN-Isak-Muivah), passed away on Tuesday, reports Zee News.

He was undergoing treatment at the prestigious Fortis Hospital in New Delhi for a "combination of illnesses". He was in his eighties.

The 85-year-old high-profile rebel Naga leader was earlier admitted to Fortis Charitable Hospital due to chest infection. Swu suffered from "pre-existing diabetes and kidney ailment'.

Founder member of NSCN, Swu, who along with Thuingaleng Muivah and S S Khaplang, raised the banner of sovereignty for Greater Nagalim outside of India.

This happened on January 31, 1980, after they opposed the Naga faction of Naga National Council for entering into an understanding with the Indian government.Negotiations between Indian and Naga leaders have been going on since a ceasefire was signed in 1997, without a solution in sight, but since then several factions have emerged.