By Tim Hirsch BBC environment correspondent

Cocaine-users across the world are helping to destroy the Amazon rainforest, Colombian Environment Minister Cecilia Rodriguez has warned.

Speaking in London, she appealed to the international community to help fund a scheme to pay poor farmers to protect trees instead of cutting them down to grow drug crops.

Much of the forest's flora and fauna is still unidentified

The comments were made at a conference looking at the threats to the Amazon and the impact of deforestation on the world's climate.

The problems of logging and cattle ranching are well known - much less widely recognised is the influence of the cocaine trade.

Eighty per cent of the world's supply of the drug comes from Colombia, and Dr Rodriguez said 70% of this was now grown in the Amazon region.

The area of former forest under cultivation has quadrupled in the last decade - coca farmers have to keep cutting down more trees as the soil is starved of nutrients within two years.

'Dramatic damage'

Dr Rodriguez said the message to the world's drug users was clear:

"I should call the attention of all consumers of cocaine that they're are harming dramatically the tropical rainforest of the world, because this is what the world needs for its oxygen."

The minister said the new Colombian Government was launching a policy called Trees for Drugs, under which poor farmers would be paid to protect the forest instead of growing coca and she called for international funding to help with this.

A wider appeal was made at the conference by the campaigner Bianca Jagger, who urged richer countries to create a fund to help South American governments preserve the Amazon.