Deforestation of the Amazon has accelerated, in recent months and is likely to increase this year for the first time in four years, says a senior Brazilian government scientist.
The rise raises questions over Brazil's assertion that its environmental policies are effectively protecting the world's biggest rain forest, the destruction of which is a major source of carbon emissions that cause 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 2007."
Nobre, whose government agency monitors the Amazon, said that 6000sq km of forest had been lost in the past four months.
That compares with about 9600sq km in the year to July, 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 27,000sq km.
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 farming remained intact, despite the recent annual declines in forest clearing.
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 could bring more settlers to untapped regions.
Nobre 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.