Reports from the Indian state of Assam say five policemen were killed and 10 others injured when a bomb blew up the bus they were travelling on.
Five of the injured are said to be in a critical condition.
Police say a remote-controlled bomb was detonated as the bus passed through the village of Maladhara, 140 kilometres west of the state capital, Guwahati.
Security officials say they suspect militants of the United Liberation Front of Assam carried out the attack.
They say a huge search operation is underway to catch the attackers.
More than 10,000 people have died in a two-decade-long rebel insurgency in Assam.
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