President George W Bush has expressed his concern at the illicit drug-growing industry in Afghanistan.
Afghanistan produces 75% of the world's opium, says a UN report
He also said the government of Hamid Karzai "lacked the capacity" to tackle the problem in Afghanistan's provinces.
Mr Bush has touted democratic changes in Afghanistan as a success in the US's war on terrorism, as the country prepares to hold elections next month.
Afghanistan is one of 22 nations listed by Mr Bush in his annual report to Congress on "major" drug-producers.
Of those, 14 countries are from Latin America and the Caribbean.
President Bush announced Thailand was being removed from the list, citing a drop in Thai opium poppy cultivation and heroin processing.
Although Canada is not on the list, he was critical of Ottawa for what he considers leniency on producers and private consumers of Cannabis.
"While the vast majority of illicit drugs entering the United States continues to come from South America and Mexico, the president expressed his continuing concerns about the flow of illicit drugs from Canada," said the White House in a statement.
Though Haiti remains on the list, President Bush credited the new interim government for its "substantive - if limited - counter-narcotics actions".
Countries certified as "majors" by Washington can attract US sanctions, but the White House said such penalties were unlikely this year.
The UN released figures earlier this year saying three-quarters of the world's opium poppy was now grown in Afghanistan.
Hamid Karzai has warned that drug-trafficking and production is helping terrorism, and the Central Bank governor reportedly said earlier this week it accounted for a third of the country's economy.
The US report noted the "good faith efforts" by the Afghan government to tackle the problem.
But added: "The president reported his concerns about the increased opium crop production and the government's lack of capacity to prevail in the provinces."
The 22 countries named in the report are Afghanistan, the Bahamas, Bolivia, Brazil, China, Colombia, Dominican Republic, Ecuador, Guatemala, Haiti, India, Jamaica, Laos, Mexico, Myanmar, Nigeria, Pakistan, Panama, Paraguay, Peru, Venezuela and Vietnam.