Opening the UN General Assembly special session on the world drug problem, Mr Annan said no country was immune from the problem, and called for an international response to stop drugs spawning crime and spreading diseases such as Aids.

Kofi Annan: 'Time for all nations to say yes to the challenge of working towards a drug-free world'

Mr Annan said the proposed political declaration which is to be put before the conference represents "quantum leap from piecemeal approaches of the past", since it addresses simultaneously those nations which produce drugs and those which consume them.

"The proliferation of drugs over the last 30 years is an example of the previously unimaginable becoming reality very quickly - a tragic reality," Mr Annan said.

"It is my hope that when historians study the history of humankind in the field of drug control they will write about the point where this trend was reversed".

Bill Clinton: 'No nation is so large and so powerful that it can conquer drugs on its own'

US President Bill Clinton picked up on the theme of international co-operation in the battle against drugs: "No nation is so large and so powerful that it can conquer drugs on its own -- none is too small to make a difference."

He also pledged US assistance for financial intelligence units dedicated to rooting out the passage of drug money, as well as praising the efforts of poorer drug-producing countries to stamp out the drugs industry within their own borders.

The conference at the UN headquarters in New York, attended by President Clinton and government ministers from more than 100 countries, is expected to endorse a plan aimed at reducing both the production of illegal drugs and the demand for them.

It will also examine the laundering of drug proceeds, and the need for more international co-operation against drugs traffickers.