The world's deforestation rate has accelerated to 6.4 million hectares a year, a new UN survey shows.

The UN Food and Agriculture Organisation (FAO) used satellite technology for the first time to map forests, finding there was a net loss of 4.1 million hectares a year between 1990 and 200 and 6.4 million between 2000 and 2005.

"Deforestation is depriving millions of people of forest goods and services that are crucial to food security, economic well-being and environmental health," said Eduardo Rojas-Briales, FAO's assistant director-general.

The figures showed that the world has lost 10 hectares (25 acres) of forest per minute over the 15-year period, mainly because of the conversion of tropical forests to agricultural land in South America and Africa.

The survey however found that the net global loss of forests over the whole period was 72.9 million hectares -- 32 percentage points lower than previously thought -- and that deforestation in Africa was lower than past estimates.

The survey showed forests now cover 30 percent of the world's landmass.