By Manikant Thakur BBC reporter in Patna

Thousands of protesters in India's northern Bihar state have fought pitched battles with police and set vehicles on fire in support of an opposition-led general strike.

Police detained more than 3,000 people across the state and around 50 were hurt in the clashes.

One of those injured in the state capital of Patna was Bihar opposition leader, Sushil Kumar Modi, who has been taken to hospital.

The strike had been called in protest at the recent killing of three civilians by police.

Several government offices and police stations were attacked.

Police fired several rounds of tear gas in Patna and used truncheons on demonstrators.

Acid attack

District police inspector-general, AC Verma, said opposition leaders had ''moved in processions, shouting slogans to enforce the strike call, in defiance of the police orders''.

In Arrah, 65 kilometres (40 miles) west of Patna, a constable was severely burned when a crowd threw acid on him.

The railway authorities stopped the movement of all trains in the state because of the strike.

About 50 protesters were hurt in the clashes

The civilians killed by police were shot dead in Patna last Saturday.

Student groups said the three youths had a dispute with a telephone booth owner and that police took them into custody and later killed them.

Police said the three were criminals killed in a shoot-out.

The National Democratic Alliance and the Communist Party of India (Marxist-Leninist) have demanded the dismissal of the government of state Chief Minister Rabri Devi.

The parties say law and order in Bihar has collapsed under the present regime.

Bihar, one of India's poorest and most populous states, is riven with caste violence, a Maoist guerrilla insurgency, clashes between rival militias and rampant corruption and kidnapping.