Amnesty International is calling for a fair and thorough government probe into the deaths of three people during a protest by farmers in western India.

The three were killed Tuesday when police opened fire on some 500 farmers demonstrating against the acquisition of land for a water pipeline project in Maharashtra state.

Witnesses say police used batons and tear gas to clear protesters from the Mumbai-Pune highway and some farmers began throwing stones at police.

Amnesty International said Wednesday that the state government should investigate “why police opened fire with live ammunition on people throwing stones.” Officials with the London-based rights group said using firearms in a lethal manner should be the absolute last resort.

Amnesty says some 80 protesters and 20 police officials sustained injuries and more than 250 demonstrators were arrested on various charges.

In recent months, India has seen a number of conflicts over land acquisition as farmers resist giving up their property for use in industrial, mining and infrastructure projects.

The Indian government is under growing pressure to balance the interests of industry and farmers through new legislation that tries to ensure farmers get fair compensation for their land and guarantees of an alternate livelihood.