Authorities say the United Liberation Front of Asom (Ulfa) -- which has been fighting for decades for independence for Assam -- killed 72 migrants from other parts of India in a string of attacks earlier this month.

It was the group's biggest strike in recent years.

"Doors for dialogue are open to all disaffected groups -- including Ulfa, who are willing to abjure violence," Singh told a news conference in Assam's Dibrugarh district, where many of the killings took place.

"(But) I would like to make it clear that there is no room for violence and it will not be tolerated."

Thousands of troops have fanned out through the jungles of eastern Assam in counter-insurgency operations against Ulfa since the killings took place.

Singh said his willingness to talk should not be seen as a "sign of weakness".

Indian officials and civilian representatives of Ulfa held talks last year to bring the rebels into direct negotiations with New Delhi.

But the talks failed to make headway, after which violence resurfaced and security forces launched fresh operations against the rebels.

The army says it has caught 13 alleged Ulfa guerrillas and destroyed several rebel camps since then. But it says most of the rebels have fled to neighbouring Myanmar.

Singh said he had urged the government of Myanmar to crack down on Ulfa rebels hiding there, and said the Myanmarese prime minister had assured him action would be taken if India gave adequate information about the rebels.