Deforestation of the Amazon has surged in recent months and is likely to rise this year for the first time in four years, a senior Brazilian government scientist said.
The rise raises questions over Brazil's assertion that its environmental policies are effectively protecting the world's biggest rainforest, whose destruction is a major source of carbon emissions that drive global warming.
"I think the last four months is a big concern for the government and now they are sending people to do more law enforcement," Carlos Nobre, a scientist with Brazil's National Institute for Space Research, told a seminar in Washington.
"But I can tell you that it (deforestation) is going to be much higher than last year."
Mr Nobre, whose government agency monitors the Amazon and gathers data, said that 6,000 square kilometres of forest had been lost in the past four months.
That compares with an estimated 9,600 square km in the 12 months ended July 31, which Brazil officials hailed as the lowest deforestation rate since the 1970s.
Brazil's government has said that policies such as more controls on illegal logging and better certification of land ownership were reducing the deforestation that has destroyed about a fifth of the forest - an area bigger than France - since the 1970s.
But environmental groups have warned that rising global commodity prices are likely to fuel more clearing of land for farms, as occurred in 2004 when Brazil recorded the highest deforestation rate of more than 27,000 square kilometres.
Mr Nobre said the cause of the recent surge was unclear, but that the major drivers of deforestation such as illegal logging and land clearing for cattle farming remained intact, despite the recent annual declines in forest clearing.
"All those drivers of change are there. The three years of reduced deforestation... did not bring by themselves a cure for illegal deforestation," he said.
Destruction of forests produces about 20 per cent of man-made carbon dioxide emissions, making conservation of the Amazon crucial to limiting rises in global temperatures.
But the government has struggled to stem deforestation, partly due to strong global demand that has made Brazil one of the world's biggest food suppliers. Environmental groups also warn that a rash of planned infrastructure projects in the coming years could bring more settlers to untapped regions.
"Infrastructure is associated with aggressive and progressive land use change," said Mr Nobre, noting that 90 per cent of Amazon deforestation occurred within 50 kilometres of roads. He also warned that continued high world oil prices were likely to result in a surge in demand for Amazon land to produce ethanol, the alternative transport fuel for which global demand is already booming.
"If oil prices keep increasing there will be an explosion of biofuel production in the Amazon, contrary to Brazilian government policy," Mr Nobre said.