Afghanistan has registered a drop in the cultivation of opium for the first time since the fall of the Taleban, the United Nations says.
In 2004, Afghanistan produced 90% of the world's opium
The area under cultivation for opium has dropped by 21%, says the head of the UN Office for Drugs and Crime.
But the actual output has not changed much and Afghanistan is still the largest producer of opium in the world, accounting for almost 90% of supplies.
The opium poppy is the raw material for producing the drug heroin.
"Obviously we're very pleased, because it's the result of restraint by farmers - an active decision which is important," said Antonio Maria Costa, director for the UN Office for Drugs and Crime.
He said there were several reasons for the decline, including government pressure and efforts to persuade farmers not to grow the crop.
But he also called on the government to remove governors in those provinces where opium cultivation has not come down.
"The governors should be punished, they aren't punished enough," the AFP news agency quotes Mr Costa as saying.
"They should be removed or jailed."
The UN has previously voiced fears that Afghanistan could turn into a "narco-state" if it failed to bring the drug trade under control.
On a visit to Washington earlier this year, President Karzai pledged to reduce opium farming by 30% during 2005.
The international community has spent millions of dollars on drug eradication programmes in Afghanistan since 2001, when the Taleban was ousted.
The BBC's Andrew North in Kabul says with little progress in tackling heroin processing operations and traffickers, the drugs trade still poses a major threat to Afghanistan's future.