BANGKOK (AP) — The cultivation of illegal opium has increased in Myanmar for a sixth successive year, fueled in part by rising demand for heroin across Asia, the United Nations said Wednesday.

The upsurge comes despite a government campaign to eradicate the crop from the Southeast Asian nation, which has won praise worldwide for taking major steps toward democratic reform after the long-ruling military junta ceded power last year.

Myanmar is the world's second-largest producer of opium after Afghanistan, accounting for about 25 percent of global poppy production, according to the U.N.

The rise in output of opium — the raw ingredient used to make heroin — was documented in the latest annual survey by the U.N. Office on Drugs and Crime.

The report said farmland under opium cultivation rose by 17 percent this year, up from about nearly 40,000 hectares (100,000 acres) in 2011 to 51,000 hectares (126,000 acres) in 2012.

Myanmar's illegal crop is farmed mostly in Kachin and Shan states. The two areas, located along the country's borders with China, Thailand and Laos, have been plagued by fighting between insurgent groups and the army.

Poppy is highly lucrative for impoverished farmers in need of cash, and the fact it can fetch as much as 19 times that of rice poses a huge challenge to government efforts to eradicate it.

The estimated 690 metric tons produced in Myanmar in 2012 was valued at roughly $359 million, the report said. That output was up from an estimated 610 metric tons last year.

"One probable factor behind the resurgence in opium production in Southeast Asia is the demand for opiates, both locally and in the region in general," the report said.

The vast majority of consumers are in China, with opiate users in East Asia and the Pacific Ocean region accounting for about one quarter of the world's total.

The swath of Southeast Asia where the borders of Myanmar, Thailand and Laos meet is known as the Golden Triangle. It produced more than half of the world's opium in 1990 and one third in 1998.

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A year later, Myanmar set out to become opium-free by 2014. That campaign had made considerable strides, but production has risen every year since 2006 as demand and prices grew.

The latest U.N. survey indicated the government has stepped up efforts to curtail output.

Citing government figures, the report said the government had eradicated poppies on about 24,000 hectares of land in 2012, compared to 7,000 hectares the previous year.

The 236 percent increase "is a significant increase on the area reported as eradicated in previous years."