Tribal separatists opposed to recent moves by armed groups in the region to end the violence against the government are thought to be behind the attacks late on Monday.

First, five local members of the ruling Congress party were injured in a powerful bomb blast at party headquarters in the main city of Guwahati, which ripped apart the roof and walls of the building.

Police had initially suspected a grenade attack, but later confirmed it was a bomb planted in a garbage bin.

"We claim responsibility for the blast," said an email from Arunodoy Dohoti, who heads a faction in the United Liberation Front of Asom (ULFA) militant group opposed to recently announced peace talks with the government.

Secondly, militants with machine guns attacked a bus on Monday evening carrying 20 paramilitary policemen in Kokrajhar district, about 220 kilometres (140 miles) west of Guwahati.

Three troopers died on the spot and another five later died of their injuries.

A further five are still in hospital,"NDFB militants opened indiscriminate gunfire from automatic weapons," a senior police official told AFP by telephone, referring to the National Democratic Front of Bodoland (NDFB) militant group.

A faction of the NDFB recently agreed to a ceasefire with New Delhi and the attack is thought to have been carried out by members opposed to the peace overtures, police said.

Both ULFA and the NDFB are fighting for independent homelands for their tribal followers in the tea and oil-rich region of Assam.