WASHINGTON, March 1 (News Agencies) - Afghanistan has toppled Myanmar as the world's top source of illicit opium, but the southeast Asian state is streaking ahead as the region's prime producer of amphetamines, the United States said Saturday, March 1.

In a major drugs strategy report, Washington backed up figures released by the United Nations last week showing an increase in poppy cultivation since the ouster of Afghanistan's former Taliban rulers.

"The size of the opium harvest in 2002 makes Afghanistan the world's leading opium producer, the report said, according to Agence France-Presse (AFP).

"Trafficking of Afghan opium and heroin refined in numerous laboratories inside Afghanistan creates serious problems for Afghanistan and its neighbors."

The International Narcotics Control Strategy Report, collated by the State Department from U.S. posts abroad, said that the area under opium cultivation in the country last year reached 30,750 hectares (76,000 acres).

The figure rose from a low of 1,685 hectares (4,160 acres) in 2001 after the Taliban, later ousted by a U.S.-led war, banned opium production.

The report nevertheless credited U.S.-backed President Hamid Karzai, who was in Washington this week, with taking a number of important early steps in a British-sponsored effort to cut drug production.

The drive has been complicated by political upheaval and uncertain security conditions. Although the report found that Myanmar was still a major source of opium, it concluded that production had declined for the sixth straight year to 630 metric tons in 2002 down 26 percent from a year earlier.

It called on the military regime in Yangon, which earns frequent criticism here for its human rights record, to carry on the fight against narcotics -- which it said had yielded "measurable results."

But the report found Myanmar delinquent in cracking down on bans on opium production in areas controlled by ethnic Wa groups.

It branded the country as Asia's top source of amphetamine-type products, and said it had not taken "significant steps" to stop the trafficking of the tablets.

President George W. Bush in January accused Myanmar of failing to adequately battle drugs production, in a body blow to Yangon's bid to shed its reputation as a "narco-state."

The decision featured in the president's annual report to Congress listing countries which fail to meet U.S. standards for combating the drugs trade, and which are therefore liable for U.S. sanctions.