Mr Singh is on a tour of a number of Indian hotspots

United Liberation Front of Assam (Ulfa) separatists recently said they would talk with the government if Assam's sovereignty was discussed.

But Mr Singh said Assam would continue to be an integral part of India.

The prime minister arrived in Assam after visiting other hotspots in Kashmir and Manipur.

Car rally

Winding up his three-day visit to north-eastern states, the prime minister said any issues could be discussed with rebels but not that of India's sovereignty over any of its states.

The BBC's Subir Bhaumik in Assam's capital, Guwahati, said Mr Singh also pledged to push for the speedy completion of border fences with Bangladesh to check the problem of illegal migration.

Mr Singh also flagged off an international car rally from Guwahati, which is set to pass through 10 countries.

In neighbouring Manipur on Sunday, Mr Singh urged militant separatists in the north-east to join negotiations with the federal government and end decades of strife.

"I am giving an open invitation to all young men and women who have taken to arms to come for talks with us so that we can usher in peace and prosperity in the north-east," he said.

"Our government is willing to talk to anybody who shuns the path of violence," he said in Manipur - one of seven states comprising India's troubled north-east.

The region is home to more than 200 ethnic and tribal communities and over 20 rebel groups fighting for greater degrees of independence or tribal rights.

The Indian army began a massive offensive against the Manipur rebel bases on the India-Burma border late last month.