Indian forces have been fighting Assam rebels for two decades

They say that the rebels also threw a grenade at the state legislative assembly buildings on Monday.

More than 30 people have been arrested for suspected links to the United Liberation Front of Assam (Ulfa).

Meanwhile efforts to open negotiations between the Indian government and the rebels seem to have failed.

Major offensive

The BBC's Subir Bhaumik in Calcutta says that joint patrols of the army and the police have been involved in fierce clashes with Ulfa rebels in the central district of Nalbari during the past two days.

One soldier and two rebels died in a clash on Sunday night near a college in Nalbari town, while two rebels were killed in another skirmish with the security forces in the village of Patharkuchi in the same district early on Monday.

Reports from Nalbari say that the army and police have launched a major offensive against Ulfa in the last three days.

Our correspondent says that Nalbari is one of the few major Ulfa strongholds that has been largely unaffected by military counter-insurgency operations in the past.

Meanwhile police in Assam's commercial capital, Guwahati, say "suspected Ulfa collaborators" were among more than 30 people arrested in the city over the last week for alleged links with the rebel group.

Suspected rebels hit back on Monday morning, when the thick security cover around the state assembly building in Guwahati was penetrated and a grenade was thrown.

Analysts say that efforts to start negotiations between the Ulfa and the Indian government by Assam's leading writer, Indira Goswami, now seem to have failed after Delhi refused to release 10 senior Ulfa leaders in jail.

Most rebel groups in Assam, including the National Democratic Front of Bodoland (NDFB), have started negotiations with Delhi.