Opium poppy production in Afghanistan reached another record high last year and Kabul must do more to stop it, a US State Department report says.
The report says that the poppy cultivation helps Taleban insurgents obtain money and weapons.
The drug trade hinders progress towards economic stability and democracy, the report adds.
Afghanistan grows nearly all of the world's opium poppy crop in an illegal trade worth billions of dollars.
"Eliminating narcotics cultivation and trafficking in Afghanistan will require a long-term national and international commitment," said the State Department.
"The Afghan government must take decisive action against poppy cultivation soon to turn back the drug threat before its further growth and consolidation make it even more difficult to defeat."
The report says production of the poppy was up more than a third on 2006 and good weather helped increase the yield of land already under cultivation.
In a report published at the beginning of February, the UN estimated that the amount of opium poppy cultivated in the volatile southern provinces would increase this year.
But the UN's assessment also predicted the overall harvest would be "similar to or lower than" last year's record-breaking level.
The UN Office on Drugs and Crime (UNODC) based its findings on interviews in almost 500 villages.
Afghanistan says it is making progress on curbing poppy cultivation by persuading farmers not to plant and through destroying poppy fields.
Acting counter-narcotics minister General Khodaidad, in an interview with Reuters news agency, said he was optimistic.
"We are doing better than last year and will have more poppy-free provinces this year," he said.
The growth in Afghanistan's opium crop began in earnest after the overthrow of the Taleban by US-led and Afghan forces in 2001.