The findings cast doubt over the future of opium eradication programmes that were successful in driving down cultivation in both countries in the decade until 2006.

With prices rising, cultivation in Laos soared 66 per cent to 6,800 hectares this year, and by 17 per cent to 51,000 hectares in Myanmar, the world's second largest producer after Afghanistan, according to UN estimates.

"Overall, opium poppy cultivation in the region has thus doubled since 2006," despite officials' reports from Laos, Myanmar and Thailand that nearly 25,000 hectares of poppies were eradicated this year, the report said.

The study estimates opium produced by Laos and Myanmar to be worth US$431 million, a third more than last year. Farm-gate prices per kg reached US$1,800 in Laos amid scarce supply, and US$520 in Myanmar. The number of people engaged in cultivation has risen in parallel with up to 38,000 "opium growing households" in communist Laos and 300,000 in Myanmar.

The rise indicates that Myanmese farmers - mainly in northeastern Shan state - would turn away from opium cultivation only if alternative livelihoods were available, the report said. "Farmers are very vulnerable to losses in income derived from opium, especially those who depend on such an income source for food security," it said.

"Furthermore, opium cultivation is generally linked to the absence of peace and security, which indicates the need for both political and economic solutions," it said.

The drugs trade is closely linked to Myanmar's long-running insurgencies in remote border areas, with ethnic minority rebels widely thought to use drug profits to fund operations.

In May the government signed a deal to wipe out opium and other drug production in Shan with several rebel groups currently engaged in ceasefire talks. The move was part of a wider 15-year plan to eradicate opium by 2014, but the UN study, which used satellite, helicopter and ground surveys, suggests that timescale is slipping away.

In the 1980s, Myanmar was the world's largest producer of illicit opium, until it was replaced by Afghanistan in 1991.

Cultivation there has been so successful that Afghanistan's poppy crop covered more than 131,000 hectares last year, 2-1/2 times more than Myanmar's this year.

But the recent revival of opium cultivation in Myanmar has prompted concern at the UN, which says wage labourers are being drawn in to work alongside smallholder farmers who depend on the crop for a living.

Last month, the United States kept Myanmar, which is undergoing a series of political reforms after decades of military rule, on its drug trafficking blacklist, accusing it of having "failed demonstrably" to fight the drug trade.

So far this year, Myanmar officials have destroyed more than three times the amount of opium poppy land as they did last year, according to the annual memorandum to Secretary of State Hillary Rodham Clinton that helps set US drug policy.

But Myanmar's counternarcotics performance is not sufficient to meet its international obligations, the document found.