Maoists have a presence in 182 districts of India
At least nine people, including six policemen, have been killed in clashes between security forces and Maoist rebels in India, officials say.
Two rebels and a civilian were also killed in the shoot-out in Gaya district of the northern Bihar state.
The fighting started when the police challenged a group of Maoists who were attempting to rob a bank, police say.
More than 6,000 people have died during the rebels' 20-year fight for a communist state in parts of India.
The rebels later managed to escape from the area after the clashes. Police are conducting a search operation.
In April, the rebels attacked a railway station, killing five policemen and a porter.
Maoists have a presence in about 22 districts of Bihar as well as in the neighbouring state of Jharkhand.
Prime Minister Manmohan Singh has said the Maoist insurgency is the "single biggest threat" to India's security.
They operate in 182 districts in India, mainly in the states of Jharkhand, Bihar, Andhra Pradesh, Chhattisgarh, Madhya Pradesh, Maharashtra and West Bengal.
The rebels say they are fighting for the rights of poor peasants and landless workers.