The United Liberation Front of Asom has denied involvement in the ongoing violence against Biharis in Assam.

But the situation will become serious and politicians should be prepared to face consequences if they plead for the cause of Hindi-speaking people, ULFA's self-styled commander-in-chief Paresh Baruah told a local daily Guwahati.

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He termed the violence as an "uprising" and said, "It is an expression of frustration of the people of Assam against their exploitation for a long time. We hope the people of the state will be able to teach a lesson to the Hindi-speaking people."

Baruah also said the Hindi-speaking people must leave Assam.

Chief Minister Tarun Gogoi had on Wednesday said the ULFA was behind the violence.

Prime Minister Atal Bihari Vajpayee on Thursday spoke to Gogoi and Rashtriya Janata Dal chief Laloo Prasad Yadav and made known his concern over the violence.

Vajpayee enquired about the steps taken by the state governments to restore normalcy, official sources said in New Delhi.

Violence erupted in Assam after the attack on Assamese train passengers in Bihar on November 11 and 12.