New Delhi - Security forces were on high alert across five Indian states for attacks during a shutdown called by Maoist rebels Monday as government troops widened an offensive in West Bengal.

Federal Home Minister Palaniappan Chidambaram issued the alert in central Chhattisgarh and eastern Bihar, Jharkhand, West Bengal and Orissa states after 12 paramilitary troopers were killed in a rebel attack at the weekend.

The Maoists declared a two-day strike beginning Monday in protest against the "war on people" in the West Bengal town of Lalgarh, where government forces launched an offensive to flush out the rebels.

The Home Ministry said it suspected the Maoist guerrillas would target economic infrastructure and public places in the states.

The rebels assaulted workers at the Purulia railway station in West Bengal and planted explosives on the tracks, disrupting rail traffic for several hours.

There were attempts to plant explosives and landmines in Lalgarh, some 200 kilometres west of state capital Kolkata, and bomb disposal squads were busy dealing with calls, the NDTV network reported.

Tribal villagers backed by the Maoists claimed to have "liberated" the Lalgarh region over the past week, killing at least 10 members of the state's ruling communist party and setting fire to its offices and police posts.

Security forces entered Lalgarh on Saturday and teams consisting of an estimated 1,500 paramilitary and police personnel were expanding operations in adjoining areas.

There were still 18 police stations under Maoist control in the Lalgarh region which the security forces were trying to reclaim.

Daily life was disrupted in the region as shops and business establishments remained closed during the shutdown. Hundreds of villagers queued up for food rations being distributed by the local administration.

On the eve of the general strike, neighbouring Orissa witnessed some violence as two Maoists were killed in combat with police in the Malkangiri district.

In Chhattisgarh's Kanker district, seven rebels were arrested on charges of murder and abduction, the PTI news agency reported.

Maoist guerrillas, who operate in 13 of India's 29 states, say they are fighting for the rights of the landless, poor and tribal people.

They usually attack police and government officials and installations and operate along a corridor stretching from Andhra Pradesh in southern India to the Nepal border in the north.

According to unofficial estimates, more than 3,000 people including rebels have been killed in Maoist violence in India since January 2005. (dpa)