Deforestation of the Amazon has fallen to its lowest levels since records began, according to data recently released by Brazil's National Institute for Space Research.

The boost for the environment comes a week after president Dilma Rousseff was criticised for weakening the forest protection measures widely credited for the improvement, and two weeks before Brazil hosts the Rio+20 Earth summit.

Using satellite imagery, the institute said 6,418 sq km of Amazon forest was stripped in the 12 months before 31 July 2011 – the smallest area since annual measurements started in 1988.

The data continues an encouraging trend. Since the peak deforestation year of 2004, the rates of clearance have fallen by almost 75%.

"This reduction is impressive; it is the result of changes in society, but it also stems from the political decision to inspect, as well as from punitive action by government agencies," Rousseff said.