Suspected Maoists killed at least six policemen and wounded dozens of people in eastern India today, police said.
The rebels fired on policemen watching a cultural show in the region's Bihar state, a senior officer said.
"The casualties may go up further. We are trying to find out the details of the attack," said Neel Mani, a senior police officer.
The rebels fired indiscriminately before fleeing on motorbikes, Mr Mani said.
Last week, the rebels killed 15 policemen in the western state of Maharashtra, in one of the biggest attacks in the state.
Thousands of people have been killed since the uprising began in the late 1960s.
Maoist rebels say they are fighting for the rights of poor farmers and landless labourers.
Security experts say their influence is growing. Prime Minister Manmohan Singh has described the insurgency as one of the gravest threats to India's internal security.
Reuters