Hundreds of tribal people backed by the Maoist guerrillas stormed the high-speed Rajdhani Express, one of the country's most prestigious passenger trains, in West Bengal on Tuesday. Police and security forces could free the train and its driver after a five-hour-long hostage drama, including a gunfight with the rebels in the forest.Maoists have stepped up violence across eastern and central India and internal security experts say it indicates a growing dominance of the insurgents in the state.The rebels raided a police station in West Bengal this month and abducted a senior official after gunning down two of his colleagues.Police officer Atindranath Dutta was held captive for two days and freed in exchange for 23 tribal women lodged in prisons for suspected Maoist links.Maoist attacks on police posts are nothing new in an area that has witnessed an anti-insurgency operation since June and the rebels have taken effective control of large swathes of the countryside.The insurgents say they are waging war on behalf of the poor and the landless against the state. The attack has raised concerns and West Bengal Chief Minister Buddhadeb Bhattacharjee said the swap was an "exception, not a norm."Security experts say the Maoists, whom Prime Minister Manmohan Singh has identified as the country's biggest internal threat, have thrown an open challenge to the authorities.In June a combined force of central paramilitary troops and state police retook control of Lalgarh, a town captured by the Maoists in West Midnapore district of West Bengal.The government began cracking down on the rebel leaders and sympathisers since then.The policeman abduction episode has apparently galvanised the communist government in West Bengal which has said it will heavily weaponise policemen and fortify its police stations. The NGOs working in Maoist-affected areas blame the government for the state of affairs.Is increasing Maoist violence in West Bengal indicative of a growing clout of the rebels?