Antonio Maria Costa, the UN anti-drug chief, said on Saturday the results from his agency's annual survey of Afghanistan's poppy crop were "very alarming".

Speaking in Kabul after presenting the survey to Hamid Karzai, the Afghan president, Costa said: "This year's harvest will be around 6,100 tonnes of opium, a staggering 92 per cent of total world supply. It exceeds global consumption by 30 per cent."

In a scathing statement, Costa said the Afghan government should take much stronger action to root out corruption.

He said governors and police chiefs of opium-growing provinces should be sacked and charged, and accused corrupt administrators of pocketing aid money.

Costa warned that the south of the country was "displaying the ominous hallmarks of incipient collapse, with large-scale drug cultivation and trafficking, insurgency and terrorism, crime and corruption".

World threat

The bulk of the increase was recorded in lawless Helmand province, where cultivation rose 162 per cent and accounted for 42 per cent of the Afghan crop.

The province is currently wracked by an upsurge in attacks by Taliban-led insurgents fighting Nato forces.

US officials say the Taliban are implicated in the drug trade, encouraging poppy cultivation and using the proceeds to help fund their campaign.

Doug Wankel, the top US anti-drugs official in Afghanistan, warned that the illicit trade in opium and heroin threatened the country's fledgling democracy.

Narco-state

Wankel said: "This country could be taken down by this whole drugs problem. If this thing gets out of hand, you could move from a narco-economy to a narco-state.

"Then you have a very difficult chance for this country being able to achieve what it needs to as a democracy and a nation representing its people."

Wankel described the drug trade, already estimated to account for at least 35 per cent of the country's gross domestic product, as a "national security threat to Afghanistan, the region and the world".