It will be at least a decade before Afghanistan ends its reliance on the drugs trade, the country's president has said.
Speaking at a press conference in London, Hamid Karzai warned against hopes of rapid progress in ending poppy production.
He told reporters it would need "at least 10 years of a strong, systematic, consistent effort" in the areas of eradication, law enforcement and help for farmers.
"I would give it a decade at least," the president said.
Despite the post-war arrival of democracy and the election of Karzai, the country remains unstable and its economy heavily reliant on the drugs trade.
With Britain leading the international efforts to reduce Afghan economic dependence on poppy production, big rises in drugs production over recent years have caused embarrassment for ministers.
There has also been criticism from some US officials that the strategy being pursued by the UK is failing to make any impact.
British troops are now set to expand their operations into the south of Afghanistan, where the bulk of Afghan opium is produced.
Foreign secretary Jack Straw said Britain had been making progress in its anti-drugs efforts, but accepted that the task was proving far larger than anticipated.
A new plan for Afghanistan, launched on Tuesday, would include benchmarks and timelines for the anti-narcotics programme, Straw said.
And the Afghan government is committing itself to an updated drugs control strategy.
"This will be a chance for nations to contribute to the newly-launched counter-narcotics trust fund," added Straw.
He also announced that Britain was giving aid worth £455m over the next three years to Afghanistan.
