"Afghanistan's agriculture, Afghanistan's economy, Afghanistan's way of life, Afghanistan's tradition and culture is being threatened by drugs," he told an international conference on his country's reconstruction.

With the production of opiates generating more than half of national income, according to UN estimates, Karzai said that "drugs in Afghanistan are undermining the very existence of the Afghan state."

"The problem for us is too huge to be able to face or challenge alone," he told hundreds of ministers and officials from more than 60 countries. "We require the international community to help us enforce the plan that we have."

He spoke of seeing one farmer destroying his crop in order to be able to plant poppies, and urged the international community "to help us fight it, to help us create alternative livelihoods for our people."

Britain, which is taking the lead international role in helping Afghanistan tackle drugs, hopes the two-day conference in Berlin will sign up to two plans.

One would be a general counter-narcotics strategy drawn up by Kabul, London and the United Nations, an official said.

The other would be an agreement between Afghanistan and its six neighbours on tighter border controls and information exchange.

Afghanistan is the world's biggest producer of poppy-derived opium used to make heroin. According to UN officials, the booming drug industry is in danger of turning the Central Asian nation into a failed narco-state.