Airports in India's restive northeast were put on high alert this week after intelligence reports that the region's main separatist group might try to hijack planes, an official said on Jan. 3.

The outlawed United Liberation Front of Asom (ULFA), which has been fighting in Assam state for a separate homeland for decades, is believed to be trying to hijack a plane to use as a bargaining chip to win the release of jailed rebels.

"The Bureau of Civil Aviation Security was asked by the Home Ministry to heighten security in all northeastern airports following the threat of a possible strike by the ULFA," civil aviation ministry spokeswoman Moushumi Chakravarty told AFP.

The home ministry issued the order on New Year's eve, she added.

Paramilitary guards at Assam's main airport in Guwahati city and eight other regional airports were urged to be more vigilant, she said, and were joined by bomb disposal squads and sniffer dogs.

The rebel group has long called for the release of five key jailed leaders as a condition for holding peace talks with New Delhi. The Indian government has refused to do so.

But nine years ago India released three Kashmiri militants in order to end a week-long siege after an Indian Airlines plane was hijacked by Islamic rebels en route from Kathmandu to New Delhi and flown to Afghanistan.

The ULFA is one of the most active rebel groups in India's northeast, where more than 50,000 people have lost their lives to insurgency since India's independence in 1947.