Central negotiators and the Nationalist Socialist Council of Nagalim (Isak-Muivah) began crucial talks in Bangkok on Saturday seeking to extend the nearly nine-year-old truce in Nagaland, amid indications that the rebels had toughen their stand to get some 'concessions' on their demands.

"Today, we have started informal discussions. Formal discussions are yet to take place. Nothing has come out yet," chief government negotiator and Union Minister Oscar Fernandes told PTI in Bangkok.

The NSCN-IM and security forces in Nagaland have been observing a truce since August 1997, when they agreed to a ceasefire. The truce has been extended every 12 months since then except last year, when it was renewed for just six months at the insistence of the NSCN-IM and further extended by another six months in February.

The current spell of the ceasefire will end on July 31.

Asked whether he was hopeful that the truce would be further extended, Fernandes said: "Talks are a continuous process. They will go on."

In its 'charter of demands,' the banned NSCN-IM has sought unification of all Naga-inhabited areas of the northeast, separate representation at the UN, and greater rights over natural resources, finance, defence and policing.

"We hope the government will give some positive response to our key demands. The extension of the ceasefire will depend on the outcome of the meeting," NSCN-IM spokesman Jhoney Dilbung told PTI.

Before coming to Bangkok for talks, Fernandes visited Nagaland last fortnight and met civil society leaders, including members of the influential Naga Hoho or apex tribal council, political leaders, and Chief Minister Neiphiu Rio and his cabinet colleagues to ascertain their views on the peace process.

The Naga Hoho said the peace process should not be held up under any circumstances and the NSCN-IM and the Centre should continue their parleys after extending the ceasefire to find a lasting solution to the Naga problem.

"The talks should not go wrong. Through a resolution, we have asked the NSCN-IM and the government to extend the ceasefire beyond July 31," Naga Hoho vice president Keviletou Kiewhou said.    

In the last meeting between the two sides, held at the Hague in the Netherlands in June, the government and the NSCN-IM are understood to have discussed the limits of flexibility within the Constitution and whether a 'sub-national constitution' could be accommodated within it.

This has become a thorny issue as the NSCN-IM has proposed negotiating a federal relationship with the country, sources said. It has suggested that the relationship between India and the Nagas should be defined by a mutually agreed settlement incorporated in the Constitution.

The government has argued the Constitution is flexible enough to take care of regional aspirations and diversities. It allows for 'asymmetrical federalism' -- different states and regions can relate to the Centre differently.