"The Brazilian government is prepared to provide information regarding the implementation of these projects' various stages," Amorim wrote. The letter was released by Brazil's foreign ministry on Friday.

Brazil's top diplomat said in Valor newspaper on Friday that construction would go ahead. "We are not going to stop doing things that are our right," he said.

The US$11.6 billion hydroelectric plants near the Bolivian border could become the latest in a series of bilateral disputes that began when Bolivia nationalized its gas industry in May last year, forcing Brazil to pay more for natural gas.

Bolivia had informed Brazil in writing that it was concerned about the project and requested a high-level meeting. It said Brazilian authorities had issued permits before studying environmental and social impacts.

The Brazilian government issued preliminary environmental permits on Monday for the two plants to be built on the Madeira River, a major tributary to the Amazon.

Among the 33 requirements imposed by environmental agency Ibama are impact studies on biodiversity and possible silt accumulation along the rivers.

With a total capacity of 6,500 megawatts, the two dams are seen as key to Brazil's power generation growth and economic development in the next decade.

Environmental activists say they would flood vast areas, including parts of Bolivia and Peru; spread malaria and other water-borne diseases; and destroy migrating fish, bird and animal wildlife and swathes of rain forest.