Afghanistan is making inroads in stemming an opium drug trade that has fuelled a growing insurgency in the war-torn country, according to an annual report on the global drug trade by the US State Department on Friday.
But the US singled out Myanmar, as well as Latin American powers Venezuela and Bolivia for having "failed demonstrably" to combat drug trafficking in their own countries.
Venezuela has become a major trafficking route for the US and Europe, while Myanmar remains the largest source of methamphetamine pills in Asia, the US said in its annual International Narcotics Control Strategy Report for Congress.
The report comes just days after the US Justice Department announced the arrest of more than 750 people in a major operation against Mexican drug smugglers over the past 21 months.
The crackdown has led to a sharp increase in violence in Mexico and kidnappings in some southern US states. The State Department last week issued a travel warning for Mexico in response.
"What you see is a government ... that is confronting these drug cartels and limiting their ability to do their business," said David Johnson, the State Department's top official for narcotics. "And the result is, unfortunately, a significant level of violence."
The report said government corruption remained a "key impediment" to further progress. As much as 90 per cent of cocaine consumed in the US comes through Mexico.
Afghanistan's opium poppy cultivation has fallen 19 per cent in 2008 from record highs in the two previous years, but the US warned that few inroads had been made in the country's most volatile southern provinces.
"The connection between poppy cultivation, the resulting narcotics trade, and funding of insurgency groups became more evident in 2008; nearly all significant cultivation now occurs in insecure areas with active insurgent elements," the report stated.
The drug trade has proven a major threat to security and economic development in Afghanistan. Because of improvements in the north, poppy cultivation is now almost exclusively limited to the country's five main southern provinces.
President Barack Obama this month ordered the deployment of 17,000 extra troops to Afghanistan, increasing the US presence to more than 45,000, in an effort to stabilise the country and combat Al Qaeda and Taliban strongholds in the south.
The report also singled out Bolivia's government for severely hampering US efforts to combat drug trafficking in the region. Relations between the two countries have ebbed over the last year, but Johnson said it was "essential" the US and Bolivia improve cooperation.
Colombia, which receives substantial aid from the US, has "consolidated" gains in the past year against a drug trade that has fuelled its own long-running conflict with leftist rebels, Johnson said.
The report identified 20 countries as major drug producers or traffickers: Afghanistan, The Bahamas, Bolivia, Brazil, Myanmar, Colombia, Dominican Republic, Ecuador, Guatemala, Haiti, India, Jamaica, Laos, Mexico, Nigeria, Pakistan, Panama, Paraguay, Peru and Venezuela.