By Subir Bhaumik BBC correspondent in Eastern India

One of the leading separatists groups in India's north-eastern region, the National Socialist Council of Nagaland (NSCN), has said it was behind the abduction of a senior official from the state of Manipur.

Naga leader Muivah wants a government apology

The NSCN's General Secretary TH Muivah told the BBC that the administrator from Manipur's Chandel district was now in his group's custody.

Security sources said the official, Yambem Thamkishore Singh, was kidnapped last week by a rebel group close to the NSCN, which has now set some conditions for his release.

The kidnapping appears to have been in response to an attack by security forces on an NSCN vehicle in which 11 rebels were killed.

The NSCN has been negotiating with the Indian government for a settlement of the four-decade long Naga insurgency for many years.

Ceasefire violation

A ceasefire between the separatists and Indian security forces has been in force for several years.

Nagas have held several violent protests

But it only applies in Nagaland and not in states such as Manipur which have a large Naga population and where the NSCN is active.

Earlier this month, Manipur police intercepted a truck carrying 11 Naga activists in the state's Chandel district bordering Burma, killing all 11.

Last week, security officials said a smaller rebel group close to the NSCN kidnapped Mr Singh.

Mr Muivah said the official will be released only if the state government apologises for the death of its 11 activists.

Mr Muivah told the BBC that Mr Singh was safe and denied reports that any demands for a ransom had been made in exchange for his safe release.

Although abductions are commonplace in India's troubled northeast, this is the first time such a senior administrative official has been kidnapped.

Conditions

Mr Muivah welcomed the Indian Prime Minister's offer to hold another round of talks with his group.

But he also said arrest warrants against NSCN leaders must be cancelled, cases against them dropped and provisions of the armed forces special powers act be scrapped.

This law gives security forces the power to raid any rebel hideout and arrest people without any warrant.

Observers say while dropping cases against NSCN activists may not be difficult for the Indian government, scrapping the special act in a region still troubled by several active separatist movements may not be possible.