Agency's latest report covering Thailand, Laos and Burma says the area poppies are cultivated on around 31,700 hectares.
United Nations officials say opium cultivation in Burma rose for the third straight year as ethnic rebel groups sell drugs to buy arms. The increase reverses past successes in cutting opium cultivation in Southeast Asia.
The U.N. Office on Drugs and Crime - UNODC - said Monday that opium poppy cultivation in Burma rose more than 10 percent in 2009 - the third successive year of growth.
The agency's latest report covering Thailand, Laos and Burma says the area poppies are cultivated on around 31,700 hectares. The increase followed a dramatic decline from 1998 to 2005 from 130,000 hectares to just over 20,300 hectares in 2006.
UNODC officials say part of the reason for the increase may be political instability in Burma, also called Myanmar. Some ethnic militia groups, such as the Wa and Kachin, are selling drugs to buy weapons to fight the government.
Burma's military has set a deadline for ethnic groups, many who have been fighting for decades for greater autonomy, to surrender their armies. News reports say some of those groups do not want to disarm and are preparing to fight.
"We had seen in preceding years dramatic declines, precipitous declines in opium poppy cultivation," said Gary Lewis, the UNODC regional representative for East Asia and the Pacific. In Myanmar, we are seeing increases in the last three to four years now totalling almost 50 percent when compared to the picture in 2006. For us, with our focus on the issue of drug control, that represents an unravelling of the process on containment and elimination."
In Burma, over one million people are said to be involved in opium production. Opium is used to make heroin.
But Southeast Asia - once known as the Golden Triangle because of opium production the border areas of Burma, Laos and Thailand - has been far surpassed by Afghanistan over the past decade.
Leik Boonwaat, UNODC country office representative in Laos, says Afghanistan now accounts for 95 percent of the global production of illegal opium.
"The total value of opium that has been produced for Myanmar -Burma - we estimate the total value is something like $104 million," said Leik. "For Laos it is $15 million, while in Afghanistan I think the total value we estimated this year at $438 million."
The UNODC says the total potential opium production in Southeast Asia has fallen from 1,435 metric tons in 1998 to just 345 metric tons in 2009, down more than 75 percent.
The UNODC says to cut production further the international community must help farming communities find alternative crops and livelihoods.