Police arrested three students from different parts of the district earlier last year on specific charges of colluding with the ULFA.

Intelligence reports said the ULFA and the outlawed National Democratic Front of Bodoland (NDFB) were planning a major strike in Assam's main city of Guwahati with at least four bombers already sneaking into the city.

Police Monday killed an NDFB bomber in an encounter in Guwahati, while two managed to escape.

On Sunday, an ULFA bomber was arrested along with a programmable time device (PTED) from Guwahati.

'The PTED was timed in such a way that once triggered the blast would have taken place in 17 minutes and was capable of causing maximum casualty,' said G.P. Singh, a senior police official.

The ULFA and the NDFB were both blamed for the Oct 30 serial bombings in Assam in which 100 people were killed and 400 injured.