BANGKOK (Reuters) -- A powerful separatist group in the eastern Indian state of Nagaland agreed on Tuesday to extend a cease-fire with the government by six months and resume peace talks soon, an Indian negotiator said.

"The cease-fire has been extended by six months," Indian negotiator K. Padmanabhaiah told Reuters after four days of talks in Bangkok.

Delegates from the National Socialist Council of Nagaland (Issac-Muivah) or NSCN (I-M) had agreed to meet government negotiators again, but no venue had been set, he said.

"We will be meeting fairly soon," Padmanabhaiah said.

More than 20,000 people have died in fighting for the independence of Nagaland, a mainly Christian state of two million people on India's far eastern border with Myanmar.

The NSCN (I-M), which was not immediately available for comment on Tuesday, has met Indian officials on several occasions since it started a cease-fire in 1997.

But there has been little progress on the central rebel demands -- the unification of Naga-dominated areas in northeast India, something fiercely opposed by other ethnic groups in the region, and ultimately independence.

The NSCN, which split into two factions in the late 1980s, has been fighting since 1947 for the freedom of millions of Naga tribesmen living in northeast India and neighboring Myanmar.

Security analysts say peace with the Nagas is crucial to a broader peace in the northeast, seven states connected to the rest of India by a thin strip of land and home to dozens of insurgent groups.