By Subir Bhaumik BBC correspondent in Calcutta

Ulfa military chief Barua (right) told the BBC it carried out the attacks

It was one of a series of blasts which rocked Assam during the day.

A fire also erupted on an oil pipeline in the neighbouring state of West Bengal.

An outlawed separatist rebel group, the United Liberation Front of Assam (Ulfa), said it was behind all the incidents.

The head of Ulfa's military wing, Paresh Barua, told the BBC that his group carried out three blasts in Assam as well as the oil pipeline blast in West Bengal.

Army called out

The fire in the gas pipeline in northern Assam's Baiganbari area was brought under control more than 10 hours after it broke out.

Parts of the 40cm pipeline, operated by the state-owned Oil India Limited (OIL), were destroyed.

The company's officials told the BBC that a huge fire erupted at Baiganbari after the explosion ripped open the pipeline which feeds a liquefied petroleum gas plant at Duliajan town, where the OIL headquarters are located.

A fire broke out in an oil pipeline near the Mahananda rail bridge in West Bengal at around the same time as the Assam blast.

The army was called out to douse the flames in the oil pipeline and the fire that threatened to engulf a passenger train near a bridge that connects the state to Assam.

Two more explosions took place on Thursday - one in the Assam capital Guwahati and the other in the western Assam town of Bongaigaon.

Six people including three policemen were injured in the blast.

Earlier this month, Ulfa rebels threw grenades at several cinema halls in Assam where Bollywood films were being screened.

A security adviser to the Assam government, Jaideep Saikia, told the BBC that Ulfa had regrouped after recent setbacks.

The attacks in Assam come as the state government, police and army are all busy coping with monsoon floods that have displaced nearly five million people.