The attack came on the eve of a visit to the country by US President George W, Bush and was one of the biggest by Maoists in recent years.

"Maoists set off a landmine in Darmagura area in Dantewada district, killing 55 people," senior police officer S.K Paswan told Reuters.

The dead were tribal members returning in trucks after attending a anti-Maoist meeting organised by the state, he said.

The state's Home Minister Ram Vichar Netam said 20 people had been seriously wounded and the death toll could rise.

Police senior superintendent Pawan Dev warned that the toll may rise as many people are injured and the nearest hospital is about 25 kilometres from where the attack took place.

Police intelligence officer Paswan said the victims were returning to their village of Konta after attending an anti-Maoist campaign in a neighbouring village.

The "public-awakening" campaign was organised by a politician. It involves peace marches in which thousands of Chattisgarh residents have been participating to combat Maoist violence.

This month alone the rebels have killed 19 security officials and more than a dozen residents in Dantewada district. Paswan said that around 100 people died in 2005 in Maoist violence in Chattisgarh state.

The official said a police party was searching the remote area for the rebels.

India's Maoists have bases in several states and have recently stepped up attacks. They say they are fighting for greater economic and social rights for tribes and landless farmers in rural areas.

Darmagura, 500 km south of the state capital Raipur, is a stronghold of Maoists who claim to be fighting for the rights of peasants and landless labourers.

Maoists, who operate in at least nine of the country's 29 states, have stepped up attacks in the past year, killing dozens of people including police.

Security analysts say New Delhi has not taken the Maoist threat in the country seriously. India's home ministry said there are about 9,300 Maoist guerrillas operating in the country. (Reuters, AFP)