The Centre is determined to put down violence perpetrated by insurgent groups in the Northeast, Home Minister P Chidambaram has said in the wake of attacks on Hindi-speaking people in Assam.

"Paramilitary forces and state police are vigilant. But despite their best efforts, incidents like this (killing of Hindi-speaking people) happened. We are determined to fight insurgency. We are determined to put down violence," he said on Wednesday.

Reacting to the reports of fresh violence in Assam, he described the killing of non-Assamese there as a matter of concern while expressing regret. "As long as insurgency in the Northeast continues to prevail, incidents like this will happen. But such incidents, when they happen, are deeply regrettable."

NDFB ultras on Wednesday killed four Hindi-speaking people at Rangapara in Assam's Sonitput district.

On infiltration from Bangladesh, the Home Minister said the government was taking measures to stop this by strengthening the border out posts (BPOs) and integrated check posts (ICPs) among other measures.

"We are continuing with the fencing...and we are networking all the border ICPs. So, I think a lot of effort has been put in and is been put in to restrict the entry of Bangladeshis into India illegally."

"Those who enter legally are being asked to go back when their visas expire. So, I think this is an ongoing exercise. There are problems and these problems are being addressed now with greater care and concern," he said.