"The region is turning into a killing field and it is quite natural to be shaken by the violence," said Apurba Das, a doctor in Assam's main city of Guwahati, hours after heavily armed tribal separatists gunned down 10 villagers in the west of the state late Tuesday.

Assam and neighbouring Nagaland state have been hit by an explosion of violence since Saturday, with 81 people killed and 217 injured in some 21 incidents of bombings and shootings.

Indian Prime Minister Manmohan Singh said yesterday he was concerned that separatist rebels behind recent explosion of violence were sheltering in Bangladesh.

"We are aware that some groups are taking shelter in Bangladesh which is a concern to us," Singh told a news conference in the western Indian city of Bombay.

"We have been talking to our friendly neighbours and it is our hope that all our friendly neighbours will not allow any of their territories for any terrorist activity," he added.

The northeast region is home to around two dozen militant and separatist groups with demands ranging from autonomy to secession.