"The Indian government has for long been exploiting Assam's natural resources and now it plans to extract oil from the Brahmaputra River. This is nothing but another clever attempt to take away local resources at the cost of our people," the United Liberation Front of Asom (Ulfa), said in a statement.

The Ulfa is an outlawed separatist group fighting for an independent homeland in Assam since 1979.

"We shall not allow such a thing to take place," the rebel group warned.

Ulfa's warning follows a 22 million dollar agreement by Oil India with Kazakhstan Caspi Shelf for a seismic survey along a 175-kilometer stretch of the Brahmaputra in Assam.

The 2,906-kilometer (1,816-mile) river -- one of the longest in Asia -- traverses Tibet, India and Bangladesh before emptying into the Bay of Bengal.

The survey is slated to begin later November and was expected to take two years.

Oil India officials refused to comment on the rebel threat, but said the idea to scout for crude under the Brahmaputra's riverbed was not based on assumptions.

"This is a proven oil rich zone and we are confident of striking crude along the Brahmaputra once exploration work begins after the survey," a senior Oil India official, who requested anonymity, said.

India produces about 30 million tonnes of crude oil annually, with Assam accounting for about five million tonnes.