Rio de Janeiro, Apr 24 (IANS/EFE): A strike Monday effectively halted work on Brazil's giant Belo Monte hydroelectric dam, a controversial project in the heart of Amazonia that has drawn bitter opposition from environmentalists and locals.

Around 80 percent of the workers are honouring the strike, the construction union said.

The strikers also blocked the only access road, preventing non-strikers from reaching the work site.

The Belo Monte Construction Consortium acknowledged that work had come to halt, but declined to estimate how many workers were taking part in the job action.

Negotiations broke down last Thursday after the workers voted to strike, the consortium said.

The strikers are demanding a tripling in their monthly food subsidy, from 100 reais ($53.20) to 300 reais ($159.60), and that workers from other parts of Brazil be given home leave every three months rather than twice a year.

The consortium countered with an offer of a 16 percent increase in the food subsidy and to expand home leave from nine to 19 days, while maintaining the six-month interval between leaves.

The strike casts new doubt on the chances the dam will be up and running by January 2015, as the Brazilian government had hoped.

Work on the $10.6 billion project began in March 2011 near the city of Altamira in Para state.

The 11.2 GW dam complex on the Xingu river would be the world's third-largest after China's Three Gorges and Itaipu, jointly operated by Brazil and Paraguay.

Environmentalists and indigenous protesters say the dam will flood 516 sq. km of jungle, displace 50,000 people and cause severe damage to the local ecosystem.

Brazilian officials insist the dam is necessary to keep pace with the country's burgeoning energy needs.