These attacks by the Ulfa have become a challenge to the Indian democracy.

Indian Home Minister LK Advani

Local police said that separatist militants carrying automatic weapons opened fire indiscriminately on a group of workers for the ruling Asom Gana Parishad (AGP) party in the Belsor area of Nalbari district.

"The militants came to the party's election office and started firing at the workers," a police spokesman said.

Six people were wounded in the attack, which has been blamed on the United Liberation Front of Assam (Ulfa).

Upsurge in violence

Earlier this week, at least seven people were killed in attacks also blamed on the separatist group.

And on Thursday, police said 16 people, including two policeman, were injured in an attack in another part of Assam.

The upsurge in violence comes ahead of elections to the state legislative assembly due on 10 May.

The AGP and India's ruling BJP are allies in the state elections.

Security has been tight during campaigning in Assam after rebel groups, including the Ulfa, threatened to step up attacks in the run up to the ballot.

However, the Indian Home Minister LK Advani said on Thursday that more attacks on AGP and BJP candidates were likely.

Speaking to journalists in Calcutta, he said: "These attacks by the Ulfa have become a challenge to the Indian democracy."

He also urged other political parties in the state to support the government in its fight against the insurgents and said India would be talking to neighbouring countries where the rebels were believed to be based.

Ulfa is the main separatist group in the region, and wants a separate homeland for the majority Assamese-speaking population.