By John Cummins
BBC News, Vienna
Ethnic armies in north Burma are reportedly buying arms with opium profits
The United Nations Office on Drugs and Crime says there has been a worrying rise in the extent of opium cultivation in Burma.
According to a new UN survey, the amount of land used for growing opium has increased by almost 50% since 2006.
The UN drugs agency says the cultivation of opium poppies has risen in Burma for the third year in a row.
This is undermining efforts to rid the country of its dependence on profits from illicit crops, it says.
Over 31,000 hectares of land are now devoted to growing opium, an increase of 11% compared to one year ago.
This is still a far cry from the 1990s, when Burma was the world's largest opium producer, part of the infamous Golden Triangle.
However the head of the UN drugs agency, Antonio Maria Costa, says "the trend is going in the wrong direction".
Mr Costa says increased instability in north eastern Burma is driving the rise in drug cultivation, with ethnic militant groups using drug profits to buy arms.
The UN agency is also warning that the region is becoming a major producer of synthetic drugs like amphetamines.
Mr Costa has called for a renewed commitment from governments and donors to tackling the drug problem in south east Asia.