Nine children and 13 women were among the dead, according to state police.

Locals said the attackers shouted "Long live the Ranvir Sena" - a reference to a banned group used by feudal landlords to terrorise peasants and lower caste Hindus.

Police said the attack was in revenge for Sunday's murder of 12 feudal landlords by what were believed to be landless farmers, in Bihar's Nawada district.

That attack in turn was thought to be in retaliation for the murder of five poor farm workers on 3 June in an ongoing caste war.

Lawless state

Extreme left-wing Maoist groups have conscripted poor farmers into their private armies which often clash with the powerful landlords in the state, which borders Nepal.

About 83% of India's one billion people are practitioners of Hinduism, which classifies its adherents into a social hierarchy of castes.

With an annual average of 5,000 reported murders, 12,000 incidents of rioting and hundreds of abductions, Bihar has earned the dubious distinction of being India's most lawless state.

Prime Minister Vajpayee wants to impose direct rule

Bihar chief minister Rabri Devi, an illiterate mother of nine, belongs to the Yadav community and is currently facing criminal charges of corruption and opposition demands to step down for failing to tackle caste violence and crime.

The caste-related killings in Bihar prompted Prime Minister Atal Bihari Vajpayee to recommend direct federal rule over the state last year.

But his proposal failed to get the required backing in Parliament because it was not supported by the Congress party, a coalition partner in the Bihar government.

However, after the latest killings, the Congress party threatened to change its position if the state does not improve the security situation.